______ difficult the problem was, he tried his best to solve it.
His wife has left him, but he behaved _______ nothing had happened.
Clearly, in a system _________ every decision is made on the basis of tradition alone, it may be difficult to achieve progress.
Suddenly it _________ to me that I should report the accident to the police.
The following chapters provide step-by-step instructions for practical _______ of genetic (基因)engineering to agriculture.
What a moving _____to see so many people offer help to these in danger!