计算（﹣2a2）2的结果是[ ]
A．2a4
B．﹣2a4
C．4a4
D．﹣4a4
答案：C
7. There is no ___________ in trying to talk him into joining us. He enjoys being alone.
A．doubt
B．wonder
C．hope
D．Point
椎一基底动脉供血不足的TCD主要表现为
A．血流速度增快
B．血流速度减低
C．血流速度正常
D．无血流
E．血流速度减低或无血流
___________ in trying to talk him into joining us. He enjoys being alone.