a report said that the world population was six billion ()the end_英语解答

a report said that the world population was six billion ()the end of the 20th cntury.为什么填by?
in为什么不可以

人气：401 ℃　时间：2020-02-15 09:29:03

解答

by the end of
到……结束时；到……时为止；在……之前
这是固定词组你需要记住
所以必须是 by
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