题目

This year’s fall in profits was not unexpected ,it is very disappointing. A.OtherwiseB.But C.However D.Nevertheless 答案：D 解析: 由题意“今年利润的下滑不是没有预料到。尽管如此，这还是非常令人失望的”可知应选D。下列生态系统中稳定性最差的是A.淡水生态系统B.陆地生态系统C.森林生态系统D.北极冻原