After -----what seemed half an hour,he came at last.

同学 你是不是把答案都写上去了.就是 after what seemed half an hour,he came at last.
after 是介词 然后 你看 从句中缺什么 缺主语 所以 it 可以排除 然后 如果是 that 或者 which的话 前面一定要给出其指代的名词性的词 然而 after 后面没有任何名词性的词 因此 这句话说明白点就是 after sth.that/which seemed half an hour 而 sth.that/which等于what 所以就填what