最常使用的射线挡块材料是()
A、蜡
B、低熔点铅
C、锡
D、铜
E、铁
参考答案：B
_______ in the regulations that you should not tell other people the password of your e-mail account. [ ]
A. What is required
B. What requires
C. It is required
D. It requires
2010年我国国内生产总值达到39.8万亿元，跃居世界第（）位。
A.1
B.2
C.3
