----- Nội dung ảnh ----- ``` 4. Having a higher birth rate than death rate can cause overpopulation. 5. We have several ways of producing energy without destroying the environment. 6. Let's build more green schools in Vietnam. 7. David had gone home before we arrived. 8. We had lunch then we took a look around the shops. 9. The light had gone out before we got out of the office. 10. After she had explained everything clearly, we started our work. ```
