괄호 안에 있는 단어중에서 어떤 것을 선택해야 맞을까요????

1.The proud businessman wanted to appear (happy/busy/rich).
He was a (vain/modest) man.

2.None of the engineers seemed to Know (what/where/when) to do.
They were(able/unable) to solve the problem

3.Donald sat next to brian (he/whom/who) was always best at math in his class.
Donald was (honest/dishonest).

죄송합니다... 귀찮게 해드려서 부탁드려요~~!!