这是没搞清必要条件和充分条件。。。

来源: 不明则问于 2010-04-26 10:52:26 [博客] [旧帖] [给我悄悄话] 本文已被阅读：次

WENXUECITY.COM does not represent or guarantee the truthfulness, accuracy, or reliability of any of communications posted by other users.