1. I used to go swimming with my friends when I was I child.

2. If you don't study hard, you will fail the exam.

3. Our summer vacation lasts for 3 months.

4. Don't forget to do all your HW before class.

5. Nam plays football very well.

41. I used to go swimming with my friends when I was a child.

42. If you don't study hard, you will fail the exam. (If + present simple, S + will + V)

43. Our summer vacation lasts three months.

44. Don't forget to do all your homework before class. (Don't forget to do sth: đừng quên làm việc gì)

45. Nam plays footbal well.