在爆炸性气体环境内，零线额定电压与相线额定电压的关系为（）。
A.相等
B.不同
C.
D.
参考答案：A
Whose picture is better, Jack's or Tom's?
Both of them are good. I think Jack draws _____ Tom． [ ]
A. as good as
B. as well as
C. better than
D. worse than
持续性葡萄胎是指葡萄胎完全排空后多长时间，血HCG持续阳性
A．3周B．6周C．9周D．12周E．14周
