A. War between 2 countries. B. Ways discovered to increase productivity. C. Migration from a continent to another continent. D. A new religion beginning to be accepted by peopl 参考答案:B 答案解析:[试题分析] 本题考查对相关细节的掌握。 [详细解答] 从人类三次重大变化中我们知道每次人口增长都与生产力、生产方式的提高有关,所以正确答案为B;A.两国之间的战争;C.人口从一个大陆向另一个大