10.In most parts of the world human problems_________(study) at that time.
问题描述：
10.In most parts of the world human problems_________(study) at that time.
答
In most parts of the world human problems (were studied)at that time.
“在大部分地区,人类的问题都是在那个时候被研究的.”
如果括号里是（not study）,才可以选择否定式.
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