采用机械供水，应有备用（）。
A、水源
B、水管
C、电动机
D、抽水机
参考答案：D
Once ___, it can never be forgotten.
A．see
B．to be seen
C．seen
D．saw
On a certain 10-question test, each question after the first question is worth 2 points more than the previous question. If the greatest number of points that can be scored on the test is 100, how many points is the eighth question worth ？（）
A．9
B．14
C．15
D．19
E．33
