异步电动机的调速方法中，只能有级调速的是（）。
A.变极调速
B.变频调速
C.变转差率调速
D.变极调速和变频调速
参考答案：A
(2013·山东，30)It's good to know________the dogs will be well cared for while we're away.
A．what
B．whose
C．which
D．that
《信行禅寺碑》的作者是？
