1. He is playing the guitar at his brother's wedding at the moment.
B: Remove "playing" and change "he" to "He is."
2. The bus will leave the station at 6 a.m every day.
C: Change "leaves" to "leave."
3. Why does she ride a bike to school when she is a very young girl?
C: Change "rides" to "ride."
4. Mr Quan doesn't go to the movies with us every morning because he is busy.
B: Change "goes" to "go."
5. There are many flower gardens in the town.
B: Change "flowers" to "flower."
6. They are playing soccer in the yard now.
C: Remove "playing."
7. Mary has breakfast at 6 o'clock.
B: Change "have" to "has."
8. It takes ten minutes to go from my house to school.
C: Change "take" to "takes."
9. I'll go and see mom and dad on their farm.
C: Change "seeing" to "see."
10. We work very hard but we have fun working together.
C: Change "hardly" to "hard."
11. I think you have fewer vacations than American students.
B: Change "few" to "fewer."
12. Many people think that students have an easy life.
D: Change "a" to "an."
13. He is playing the guitar at his brother's wedding at the moment.
No error.
14. The bus leaves the station at 6 a.m every day.
No error.
15. Why does she ride a bike to school when she is a very young girl?
No error.
16. Mr Quan doesn't go to the movies with us every morning because he is busy.
No error.
17. At the moment, Mr Hieu is playing soccer with his children in the yard.
B: Change "plays" to "is playing."
18. Listen to the boy! He is singing an international song on T.V.
B: Change "sing" to "singing."
19. Now, she is writing two letters to her parents in the countryside.
No error.
20: Khoi My is listening to an English song on T.V at present.
B: Change "listen" to "listening."
21. Miss Lien doesn't go to class late every morning.
C: Change "late" to "late."