Exercise 3.
1. tells
2. helps
3. swim
4. dance
5. travels
6. is listening
7. is raining
8. works
9. isn’t working
10. is running – wants
11. has learned
12. has taught
13. has worked
14. haven’t eaten
15. has gone
`→` thì hiện tại đơn : S + V(s/es) + O
`→` thì hiện tại tiếp diễn : S + am/is/are + V_ing
`→` thì hiện tại hoàn thành : S + have/has + V3/ed + O