The strongest people 主语
are 谓语系动词
those who can hold a lot of things inside but act like nothing happened. 后面一个并列式的短语做表语.who can hold a lot of things inside是修饰什么的The strongest people这句话是A（B）+C的句式么？but 在句中做转折词用，所以后面的整个短语属于并列短语，分解成句中就是
The strongest people can hold a lot of things inside but he can act like nothing happened.
这个句子就是个主系表结构，后面的并列短语作表语用，非A(B)+C的句式