Exercise 1:

1. rises, sets

Điều hiển nhiên nên dùng thì HTĐ

2. is

often → HTĐ

3. listening

enjoy + V_ing

4. boils

Điều hiển nhiên nên dùng thì HTĐ

5. to go

S + V + noun + enough + for sb + to V

6. studying

prefer + V_ing

7. doing

S + spend + time + V_ing

8. received 

last week → QKĐ

9. left

two years ago → QKĐ

10. watched

last summer → QKĐ

Exercise 2:

1. She is not old enough to go to school alone

2. She isn't old enough to ride a motorbike 

3. I am lucky enough to have many good friends

4. Those apple aren't ripe enough for we to eat them

*Cấu trúc enough: S + be + adj + enough + for sb + to V