several million 后边啥时候加of :many能修饰million吗?

关于several million,many million several million of 和several millions of several millions of 还是several million several million of可以用吗?这么用对吗? several million要不要加S? “million”哪些时候加“s”? several后面加hundred 和million 是咋变 在哪加s 加了of呢 具体是several millions of students还是several million students several million people还是several millions of people问什么 several million people这个, many后加million用什么形式 有many million这样表示的吗