配电变压器是利用电磁感应原理工作的,所以可以改变()
A.电压
B.频率
C.波形
参考答案:A
— Do you think it wise for Chinese mothers to try to do everything for their children?
— No, that’s ______ they are mistaken.
A.where
B.when
C.so
D.how
钢筋工程中,钢筋焊接的焊机一般常用()、()、()。