《煤矿安全规程》规定：采取有效措施控制尘，毒危害，保证作业场所符合国家（）标准。
A.防尘降尘
B.文明生产
C.职业卫生
D.安全生产
参考答案：C
家兔的妊娠期为（）天。
A.32
B.42
C.22
D.52
All my friends like shopping in that supermarket. I wonder how long it _____. [ ]
A. has opened
B. has been open
C. has been opened
D. opened
