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。
The letter failed to be posted because he wrote the address _____________ (correct).
Did his parents buy _____________ (they) a big cake for their twenty years of marriage?
The old man couldn’t be __________ (glad) to know that he finally passed the driving test.”
Though I have read about three _____________ (four) of the novel, I still can’t guess the ending of it.