1. (-) He didn't write a book.
(?) Did he write a book?
2. (-) She wasn't my boss.
(?)Was she your boss?
3. (+) They built a new house.
(?)Did they build a new house?
4. (+) I was at the concert last Sunday.
(?)Was you at the concert last Sunday?
5. (+) I bought.
(-) I didn't buy.
( câu 5 có thiếu gì không ạ)