【单选题】设信号的波特率为500Baud,采用幅度-相位复合调制技术,由4种幅度和8种相位组成16种码元,则信道的数据速率为()。
【单选题】下列关于巨幼红细胞贫血的描述,不正确的是
E.
人体内贮存的维生素B12可供人体使用3-6年
【单选题】Mark suggests that they ____.
A.
eat their picnic in about 10 min
B.
move over to the bank and eat their picnic
C.
move over to the bank and stop for a while
D.
eat their picnic while travelling along the river
【单选题】Mark suggests that they _____.
A.
eat their picnic while travelling along the river
B.
move over to the bank and stop for a while
C.
eat their picnic in about ten minutes
D.
move over to the bank and eat their picnic
【单选题】弹簧由于在交变应力下工作,除应有高的强度和弹性外,还应有高的:
【单选题】弹簧在交变应力下工作,除应有高的强度和弹性外,还应有高的( )。
【简答题】已知抛物线G的顶点在原点,焦点在y轴正半轴上,点P(m,4)到其准线的距离等于5, (Ⅰ)求抛物线G的方程; ( Ⅱ)如图,过抛物线G的焦点的直线依次与抛物线G及圆x 2 +(y-1) 2 =1交于A,C,D,B四点,试证明|AC|· |BD|为定值; (Ⅲ)过A,B分别作抛物线G的切线l 1 ,l 2 ,且l 1 ,l 2 交于点M,试求△ACM与△BDM面积之和的最小值.