1·The rule is that you pluralise the "head" of the term.
名词词组复数变化的规则就是：变“重点词”。
2·But English is pretty simple: verbs hardly conjugate; nouns pluralise easily (just add "s", mostly) and there are no genders to remember.
但英语其实很简单：基本没有动词变位，名词变复数很容易(大多数情况下只用加字母“s”)，而且无需记忆词性。