Dùng V_ing khi:  

* Được dùng cho các mệnh đề chủ động
Ví dụ:
- The woman who is standing over there is my mother.
=> The woman standing over there is my mother. 

- Dùng V_ed khi:

Được dùng cho mệnh đề bị động
Ví dụ:
- I love songs which were presented by Maroon 5.
=> I love songs presented by Maroon 5.

- Dùng to V khi

*Dùng khi đứng trước các từ bổ nghĩa như: only, first, second, last...only
Ví dụ:
- He is the last person who left the office.
=> He is the last person left the office.

*Động từ have/had:
Ví dụ:
- He had something that he could/had to do
=> He had something to do.

* Đầu câu có here(be), there(be)
Ví dụ:
- There is a deadline which have to be done today.
=> There is a deadline to be done today.