18. This work has to be finished on time

Động từ khuyết thiếu : S + ĐTKT + be + P2

19. It took two hours to correcting their excercises

S + spend + time/money + V-ing.

It takes/took (sb) + time + to do something 

20. She began working in this factory since the begining of this year

S + begin (began) + Ving + thời gian 

5 sao + cảm ơn + ctlhn nha

18.This work must be finished on time

----> Cấu trúc câu bị động dạng động từ khuyết thiếu:

                S + must + be + PII....

    (have to = must nhé)

19.It took them two hours to correct their exercises

----> Cấu trúc : It takes (took ở dạng QKĐ) + thời gian + to V..

20.She began working in this factory since the begining of this year

----> Cấu trúc : S + begin (began) + Ving ...... + thời gian (ý là từ lúc nào)