呈不规则板片状,边缘不整齐,色泽鲜艳,光亮如镜,习称( )
A.“珠宝砂”B.“镜面砂”C.“豆瓣砂”D.“钉头”E.“硬滑石”
参考答案:B
It's raining heavily outside. He has to stay at home, ______? [ ]
A. has he
B. hasn't he
C. does he
D. doesn't he
在不变损耗和可变损耗相等条件下,变压器效率最高。