常用作烷基化反应的溶剂有哪三类（）。
A.非极性溶剂
B.极性溶剂
C.半极性溶剂
D.中等性质溶剂
参考答案：A, B, D
Not until he went through real hardship _____the love we have for our families is important.
A．had he realized
B．did he realize
C．he realized
D．he had realized
对于（）可直接丈量或用探杆、测绳进行探测。
A.洞口面积
B.不可见洞深
C.可见洞深
D.洞穴体积
