1. I will tell you about it when I come home from my holiday.
2. My teacher has teached English at this school for six years.( for + time -> present perfect)
3. The number of students in my class is fifty.
4. Smoke is not good for our health.
5. Why do you cry ?
Xin lỗi mấy câu khác mình không biết giải thích ntn.