单选题
According to the passage, early humans ______.
A、
were less selfish than the present-day people
B、
were more co-operative in nature
C、
had to be co-operative to survive
D、
had to behave better than the present-day people
【正确答案】
C
【答案解析】
本题是细节题，我们可从原文中找到对应：For social groups to work，individuals had to co-operate，rather than act selfishly．其他选项均不符合文意。
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