为了查明岩溶通道中的地下水的运动规律，通常采用方法简便、效果又好的（）。
参考答案：连通试验
--Have you paid? What’s my share of the bill?
-- . It wasn’t very much.
A．Don’t worry about it.
B．It’s my share
C．None of your business.
D．It’s up to you.
If the policemen had arrived two minutes later than that, the man must have been killed by the gang.
A. Had the policemen arrived B. If the policemen arrivedC. If the policemen arrived D. Had the policemen had arrived
