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阅读理解。根据短文内容,判断正(T) 误(F)。 We are all busy talking about and using the Internet,but how many of us know the history of the Internet?Many people are surprised when they find that the Internet was set up in the 1960s.At that time,computer networks didn't work well.If one computer in the network broke down, then the whole network stopped. So a new network system had to be set up.It should be good enough to be used by many different computers.If part of the network was not working,information could be sent through another part.In this way computer network system would keep on working all the time,I'm daydaytest Placeholder At first the Internet was only used by the government, but in the early 1970s, universities, hospitals and banks were allowed to use it, too. However, computers were still very expensive and the Internet was difficult to use.By the start of the 1990s,computers became cheaper and easier to use.Scientist had also developed software (软件) that made 'surfing' the Internet more convenient (方便的). Today it is easy to get on-line and millions of people use the Internet every day. Sending e-mail is more and more popular among people. The Internet has now become one of the most important parts of people's life. (     )1. The Internet has a history of less than thirty years. (     )2. In the 1960s computer networks went wrong easily. (     )3. Scientists set up a new network system to make computers cheaper. (     )4. I'm daydaytest Placeholder!People didn't have enough software to get on-line conveniently until the early 1990s. (     )5. The Internet is only easily used by governments,banks,offices and universities.
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【单选题】函数f(x,y)=4(x−y)−x2−y2f(x,y)=4(x−y)−x2−y2的极值为
A.
f ( 2 , − 2 ) = 8 " role="presentation" style="display: inline-block; line-height: 0; font-size: 19.52px; overflow-wrap: normal; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; color: rgb(0, 0, 0); font-family: "Microsoft YaHei"; position: relative;" > f ( 2 , − 2 ) = 8 f(2,−2)=8
B.
f ( − 2 , − 2 ) = 0 " role="presentation" style="display: inline-block; line-height: 0; font-size: 19.52px; overflow-wrap: normal; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; color: rgb(0, 0, 0); font-family: "Microsoft YaHei"; position: relative;" > f ( − 2 , − 2 ) = 0 f(−2,−2)=0
C.
f ( 2 , 2 ) = 0 " role="presentation" style="display: inline-block; line-height: 0; font-size: 19.52px; overflow-wrap: normal; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; color: rgb(0, 0, 0); font-family: "Microsoft YaHei"; position: relative;" > f ( 2 , 2 ) = 0 f(2,2)=0
D.
f ( − 2 , 2 ) = 8 " role="presentation" style="display: inline-block; line-height: 0; font-size: 19.52px; overflow-wrap: normal; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; color: rgb(0, 0, 0); font-family: "Microsoft YaHei"; position: relative;" > f ( − 2 , 2 ) = 8 f(−2,2)=8
【简答题】基准分为()基准和()基准两大类;工艺基准有()基准,()基准和()基准.
【单选题】(2009年) 设z=f(x2一y2),则dz等于( )。
A.
2x一2y
B.
2xdx一2ydy
C.
f’(x2一y2)dx
D.
2f’(x2一y2)(xdx—ydy)
【单选题】已知点P 1 (x 1 ,y 1 )、P 2 (x 2 ,y 2 )分别在直线l上和在l外,若直线l的方程为f(x,y)=0,则方程f(x,y)-f(x 1 ,y 1 )-f(x 2 ,y 2 )=0表示(  )
A.
与l重合的直线
B.
与l平行,且过P 1 的直线
C.
与l平行,且过P 2 的直线
D.
同时过P 1 、P 2 的直线
【单选题】函数f(x,y)=(6x−x2)(4y−y2)f(x,y)=(6x−x2)(4y−y2)的极值为
A.
f ( 3 , 2 ) = 36 " role="presentation" style="display: inline-block; line-height: 0; font-size: 19.52px; overflow-wrap: normal; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; color: rgb(0, 0, 0); font-family: "Microsoft YaHei"; position: relative;" > f ( 3 , 2 ) = 36 f(3,2)=36
B.
f ( 3 , 0 ) = 0 " role="presentation" style="display: inline-block; line-height: 0; font-size: 19.52px; overflow-wrap: normal; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; color: rgb(0, 0, 0); font-family: "Microsoft YaHei"; position: relative;" > f ( 3 , 0 ) = 0 f(3,0)=0
C.
f ( 0 , 2 ) = 0 " role="presentation" style="display: inline-block; line-height: 0; font-size: 19.52px; overflow-wrap: normal; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; color: rgb(0, 0, 0); font-family: "Microsoft YaHei"; position: relative;" > f ( 0 , 2 ) = 0 f(0,2)=0
D.
f ( 3 , 2 ) = 6 " role="presentation" style="display: inline-block; line-height: 0; font-size: 19.52px; overflow-wrap: normal; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; color: rgb(0, 0, 0); font-family: "Microsoft YaHei"; position: relative;" > f ( 3 , 2 ) = 6 f(3,2)=6
【简答题】已知函数f(x)=(x 2 ﹣a)e x . (1)若a=3,求f(x)的单调区间和极值; (2)若x 1 ,x 2 为f(x)的两个不同的极值点,且 , 若 恒成立,求实数b的取值范围.
【简答题】设F(x,y)是一个二维随机向量(X,Y)的分布函数,x12,y12,证明: F(x2,y2) - F(x1,y2) - F(x2,y1)+F(x1,y1)≥0.
【单选题】机体抵抗病原生物感染的功能称为
A.
免疫监视
B.
免疫自稳
C.
免疫耐受
D.
免疫防御
E.
免疫调节
【简答题】工艺基准有工序基准、( )、测量基准和装配基准之分。
【判断题】工艺基准有工序基准、 定位 基准 、 测量基准和装配基准之分
A.
正确
B.
错误
相关题目:
【单选题】函数f(x,y)=4(x−y)−x2−y2f(x,y)=4(x−y)−x2−y2的极值为
A.
f ( 2 , − 2 ) = 8 " role="presentation" style="display: inline-block; line-height: 0; font-size: 19.52px; overflow-wrap: normal; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; color: rgb(0, 0, 0); font-family: "Microsoft YaHei"; position: relative;" > f ( 2 , − 2 ) = 8 f(2,−2)=8
B.
f ( − 2 , − 2 ) = 0 " role="presentation" style="display: inline-block; line-height: 0; font-size: 19.52px; overflow-wrap: normal; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; color: rgb(0, 0, 0); font-family: "Microsoft YaHei"; position: relative;" > f ( − 2 , − 2 ) = 0 f(−2,−2)=0
C.
f ( 2 , 2 ) = 0 " role="presentation" style="display: inline-block; line-height: 0; font-size: 19.52px; overflow-wrap: normal; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; color: rgb(0, 0, 0); font-family: "Microsoft YaHei"; position: relative;" > f ( 2 , 2 ) = 0 f(2,2)=0
D.
f ( − 2 , 2 ) = 8 " role="presentation" style="display: inline-block; line-height: 0; font-size: 19.52px; overflow-wrap: normal; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; color: rgb(0, 0, 0); font-family: "Microsoft YaHei"; position: relative;" > f ( − 2 , 2 ) = 8 f(−2,2)=8
【单选题】函数f(x,y)=(6x−x2)(4y−y2)f(x,y)=(6x−x2)(4y−y2)的极值为
A.
f ( 3 , 2 ) = 36 " role="presentation" style="display: inline-block; line-height: 0; font-size: 19.52px; overflow-wrap: normal; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; color: rgb(0, 0, 0); font-family: "Microsoft YaHei"; position: relative;" > f ( 3 , 2 ) = 36 f(3,2)=36
B.
f ( 3 , 0 ) = 0 " role="presentation" style="display: inline-block; line-height: 0; font-size: 19.52px; overflow-wrap: normal; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; color: rgb(0, 0, 0); font-family: "Microsoft YaHei"; position: relative;" > f ( 3 , 0 ) = 0 f(3,0)=0
C.
f ( 0 , 2 ) = 0 " role="presentation" style="display: inline-block; line-height: 0; font-size: 19.52px; overflow-wrap: normal; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; color: rgb(0, 0, 0); font-family: "Microsoft YaHei"; position: relative;" > f ( 0 , 2 ) = 0 f(0,2)=0
D.
f ( 3 , 2 ) = 6 " role="presentation" style="display: inline-block; line-height: 0; font-size: 19.52px; overflow-wrap: normal; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; color: rgb(0, 0, 0); font-family: "Microsoft YaHei"; position: relative;" > f ( 3 , 2 ) = 6 f(3,2)=6