金元醫家刘完素的学术思想是（）
A.火热论
B.攻邪论
C.脾胃论
D.滋阴论
参考答案：A
_____ to make a speech, he said he would be glad to.
A．When asked
B．When asking
C．When he was asking
D．When to ask
对称三相电势在任一瞬间的（）等于零。
A.频率
B.波形
C.角度
D.代数和
