根据句意，在答卷标有题号的横线上，写出括号内所给单词的适当形式。

根据句意，在答卷标有题号的横线上，写出括号内所给单词的适当形式。
小题1:The letter failed to be posted because he wrote the address _____________ (correct).
小题2:Did his parents buy _____________ (they) a big cake for their twenty years of marriage?
小题3:The old man couldn’t be __________ (glad) to know that he finally passed the driving test.”
小题4:Though I have read about three _____________ (four) of the novel, I still can’t guess the ending of it.