He is sure that he can do better.他确信他能够做的更好.
She can't remember which seat is hers.她记不得哪一个是她的座位了.
I don't know who you are.我不知道你是谁.
The teacher wants to know whose shirt it is.老师想知道这是谁的衬衣.
whom是引导定语从句的.
OK?希望能帮到你啊!