交流弧焊机的二次额定工作电压为()左右。
A.30V
B.70V
C.220V
D.380V
参考答案:A
It is reported that the United States uses_________ energy as the whole of Europe.
A.twice as
B.twice as much
C.twice as many
D.much twice as
维持血钙正常水平最重要的调节因素是()
A.甲状旁腺激素
B.降钙素
C.维生素D
D.1,25-(OH)2-D3
E.甲状腺素