在纯电阻正弦电路中，电压与电流的相位差是（）。
A、90
B、0
C、180
D、-90
参考答案：B
Our music teacher has won the first prize in the competition. We’re very _______ him.
A．angry with
B．proud of
C．famous for
D．good at
A型人参皂苷的苷元是
A．人参二醇
B．20(-原人参二醇
C．齐墩果酸
D．人参三醇
E．20(-原人参三醇
