实验室中下列物质因没有密封保存而使质量减少的是[ ]
A．浓硫酸
B．生石灰
C．烧碱
D．浓盐酸
答案：D
函数f（x）=x3-3x的极大值点是（ ）
A．-2
B．-1
C．1
D．2
In an appropriate communication model between a sender and a receiver．all the following statements are correct EXCEPT：
A．Noise should be minimize
B．Receiver must decode and reply back to the messag
C．Receiver should acknowledge and agree with the message sent by the sende
D．Sender must choose right way to send the message
