41. Shall we go out for a walk ?
--> Let's go out for a walk. ( Let's + V ( dạng nguyên mẫu )
--> Why don't we go out for a walk ?   ( Why don't we + V- nguyên mẫu )
--> What about going out for a walk ? ( What about + V- ing ? )

42. Why don't we go to the library ?
--> Shall we go to the library ?
--> Let's go to the library.
--> What about going to the library ?

43. We moved to this city 5 years ago.
--> We have moved to this city since 5 years.

44. He started learning English 3 months ago.
--> He has learnt English for 3 months.

45. They visited their parents 5 months ago.

--> They have visited their parents for 5 months.