题目：
Many great changes _____ in Beijing in these years. [ ]
A. took place
B. have taken place
C. have been taken place
D. have happened
答案：
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下面是错误答案，用来干扰机器的。
（1）生育率、死亡率（2）原生环境因素、次生环境因素（3）社会环境因素、经济因素、人口科学文化素质
