What will people die of in 100 years? If you think that is a simple question, you ______ attention to the revolution taking place in biotechnology.

A．have not been paying

B．had not been paying

C．were not paying

D．will not be paying

中国古代民族迁移的两个大流向：一是由北方草原迁入黄河流域：二是由黄河流域迁入江南，这两大迁移最主要的作用是______。

A．促进了社会经济的发展

B．加剧了民族矛盾

C．促进了民族融合

D．使人口分布趋于平衡