一般抹灰使用的块状生石灰须经熟化成石灰膏才能使用，在常温下，熟化时间不应少于( )；用于罩面的石灰膏，在常温下，熟化的时间不得少于( )。
A. 10天，20天
B. 12天，24天
C. 15天，30天
D. 16天，25天
According to the passage water is important for all of the following, except______.
A. early international trade
B. the most common substance in living plant and animal tissues
C. hydroelectric power stations
D. sanitation and recreation
According to the author, technical terms are used because ______.
A. they describe a process in details
B. they can only be understood by people of a given profession
C. they can be found in almost every dictionary
D. they can be universally understood by people of a given profession
采用双机抬吊作业时，每台起重机荷载不得超过允许荷载的( )，且应对每一吊进行试吊作业，施工中必须保持两台起重机同步作业。
A. 60%
B. 70%
C. 80%
D. 90%
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