我国工业生产和生活的交流电的频率是(),称为工频。
A.100Hz
B.50Hz
C.40Hz
D.20Hz
参考答案:B
--- Look at ______ book on the desk . Is it ______ useful one ?
--Yes, it is . In the book there is much advice on how to learn math well.
A.a, the
B.the, a
C.the, an
D.a, an
以下属于常用中成药非处方药的是()
A.柏子养心丸
B.乐脉颗粒
C.狗皮膏
D.木香槟榔丸
E.养血安神丸