长期以来，由于我们在草原上________，对森林________，对动物________，再加上环境污染等因素的影响，不少动植物已经绝种或者将要灭绝。

Although the old man was ______ death, he still fought with the disease bravely. 　

A．at the end of　

B．on the top of

C．at the edge of　

D．on condition that