good point,and u got it; i was wondering that 2,

来源: 于 2009-08-05 14:15:25 [博客] [旧帖] [给我悄悄话] 本文已被阅读：次

this is why i did not have the answer, and did not know how to answer that question, actually myself.

it was in a toefl prepa book N years ago.