-They often enjoyed going to the zoo -Peter always visited his grandma when he was not married -> chuyển thành câu phủ định và nghi vấn

`1.` 

(`-`) They didn't often enjoy going to the zoo

( `?` ) Did they often enjoy going to the zoo?

`2.` 

(`-`) Peter didn't always visit his grandma when he was not married.

( `?` ) Did Peter always visit his grandma when he was not married? 

`@` QKĐ `-` V thường :

(`+`) S Ved O

(`-`) S didn't V

( `?` ) Did S V?