Here are the corrections for each sentence:

46. **Corrected:** At recess, the students **practice** basketball.
- **Mistake:** "practice to play" should be corrected to "practice."

47. **Corrected:** She will tell him your message as soon as he **comes** back.
- **Mistake:** "came" should be corrected to "comes" to match future tense.

48. **Corrected:** Each of you **has** a share in the work.
- **Mistake:** "have" should be corrected to "has" because "each" is singular.

49. **Corrected:** The public library in the city has **thousands** of good books.
- **Mistake:** "thousand" should be corrected to "thousands" because it refers to multiple books.

50. **Corrected:** Ba **is** in class 7A and he enjoys **school** **very much**.
- **Mistake:** "the school" can be corrected to "school" for a more natural expression.