` 6.` He stopped to smoke => smoking because cigaretes are harmful for his health.
`7.` I am never boring => bored When I learn English
`8.` When I'll go back => I go back to my country, I'll write to you
`9.` The picture was painting => was painted by Michael last year.
`10.` Mr. Smith is going to buy a new Japanese car, doesn't he  => isn't he
`11.` Although Mrs. Thoa was tired, but => bỏ she helped Tuan with his homework.
`12.` All the students are looking forward spending => to spending their free time.

`6`.  A stopped to smoke `->` stopped smoking

`->` stop + Ving: dừng hẳn việc đang làm

`7`. C boring `->` bored

`->` Chủ ngữ chỉ người mang nghĩa bị động cần tính từ thêm -ed

`8`. B I'll go back `->` I go back

`->` When + hiện tại đơn, tương lai đơn

`9`. B was painting `->` was painted

`->` Câu bị động quá khứ đơn: S + was/were + Vpp

`10`. D doesn't he `->` isn't he

`->` Câu hỏi đuôi thì tương lai gần, vế trước khẳng định vế sau phủ định

`11`. B but `->` bỏ

`->` Although và "but" không đi chung câu

`12`. C spending `->` to spending

`->` loook forward to V: mong chờ