6. Because of his weakness, Chau couldn't lift the box.

because of + N/ Ving / Np, clause: bởi vì 

7. Let's buy another armchair.

Let's + V1: đưa ra ý kiến, đề nghị

8. The front yard isn't large enough to play football in.

S + be (not) + ADJ + enough + (for O) + to V: (không) đủ .. để làm gì 

9. How old is your father?

How old + be + S?

= What + be+  one's age? hỏi tuổi

10. We are close friends although we have different characters.

clause + although + clause: mặc dù 

`color{orange}{~LeAiFuRuiHuiBao~}`