$1.$ We have known each other since we were students.

- S + have/ has + V3 + since ...

$2.$ I am not as hard-working as my sister.

- (not) + as + adj + as.

$3.$ How much does this watch cost?

- How much = What is the price: Hỏi giá tiền.

$4.$ Can you tell me how to go to Dong Nai post office?

$5.$ There aren't any bottles on the shelf.

- "any" ở trong câu phủ định, có thể dùng với danh từ đếm được.

$6.$ We don't have enough time to prepare the speech.

- S + (not) + V + enough + noun + (for sb) + to V.

$7.$ When did you start learning English?

$8.$ I started doing this job ten years ago.

- S + have/ has + V3 + for +  time = S +  started + V-ing + time + ago.

$9.$ They haven't met each other since last summer.

- S + last + V2 + time =  S + haven't/ hans't + V3 + since ...

$10.$ If you are not careful, you will hurt yourself.

- If + S + V (s/es), S + will + V.

$11.$ I am not as tall as your brother.

- as + adj + as.

$12.$ There are not any carrots in the market.