主要是有个语序和被动语态的问题。
China claims that the birth rate has been （出生率一定是被控制，用被动语态）effectively controlled since the family planning policy was implemented in 1979.
按你原来的语序，会被误解为从1979年开始中国就在声称有效控制了出生率。
Since from 1979 China claimed the implementation of family planning policy,Chinese has effectively control the birth rate.
这样应该是对的，你那一句我不确定
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