情景对话

A：Would you like to have dinner with me this evening, Bob? 

B： ____ . Maybe another time.

A：What are you doing?

B：I'm making aplan____

A：What plan? Is it very important?

B：Yes, I always do volunteer work on the first Saturday of every month.

A：____

B：I help out at the children's hospital. I help to plan some activities.

A：____

B：Of course. You should help to make the sick children happy.

A：____ I can tell them some interesting stories.

a. Oh, I'd love to do that.

b. I must finish it on time.

c. Sorry, I can't. I'm busy.

d. Err…Bob, could I join you?

 e. What kind of volunteer work do you do？

一个按正弦规律变化的交变电流的图象如图所示，由图可知（   ）

①该交变电流的频率为0.2Hz；

②该交变电流的有效值为14.1A；

③该交变电流的瞬时值表达式为i=20sin0.02tA；

④t= $\frac{T}{8}$ 时刻，该交变电流大小与其有效值相等．