关于several million,many million

关于several million,many million several million people这个, several millions of 还是several million several million of 和several millions of severall为什么后接million不用复数?several难道是具体数字?还有many为什么不能接million这 many million people several million要不要加S? 关于million的用法 具体是several millions of students还是several million students several million people还是several millions of people问什么 many后加million用什么形式 有many million 这种用法么