皮皮学，免费搜题
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【单选题】
What do we know about silk today?A.
[A]It is very popular among painters.
B.
[B]It is much cheaper than in the past.
C.
[C]It is used by famous dress designers.
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举一反三
【单选题】已知f 1 (t)=u(t),f 2 (t)=e -at u(t),可以求得f 1 (t)*f 2 (t)=():
A.
(1-e -at )u(t)
B.
e -at u(t)
C.
(1-e -at )u(t)
D.
e -at u(t)
【多选题】The Grand Canal was helpful in________.
A.
national unity
B.
economic development
C.
protecting the environment
D.
boosting the local agriculture
【单选题】The Grand Canal was first excavated in ________.
A.
the Han Dynasty
B.
the Warring States period
C.
the Spring and Autumn Period
D.
the Sui Dynasty
【单选题】Mass media was born. And this ________ a whole new world.
A.
open
B.
open up
C.
opened up
D.
opened
【单选题】The Grand Canal began to be dug in _____.
A.
the Spring and Autumn Period
B.
the Sui Dynasty
【单选题】已知f1(t)=2[u(t+1)-u(t-1)],f2(t)=u(t)-u(t-2),若f(t)=f1(t)*f2(t),则f(0)=( )。
A.
1
B.
2
C.
3
D.
4
【单选题】已知f1(t)=u(t),f2(t)= ,则f1(t)与f2(t)的卷积f1(t)*f2(t)为()
A.
(1-e )u(t)
B.
(e -1)u（t）
C.
(e -1)u(t)
D.
(e +1)u（t）
【简答题】国家及地区顶级域被IANA委托给国家性的域名注册局来管理,比如德国的DENIC、英国的Nominet、中国大陆的CNNIC,类似于“www.shujugo.cn”中的.CN类英文域名,注册局为CNNIC,其中文全称是____。
【简答题】能源类型的分类,并举例。
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