`1,` Mr. Phong was the first person whose advice I asked for.

- whose là ĐTQH chỉ sự sở hữu, whose + N

- ask for advice : xin lời khuyên

`2,` Water pollution leads to the death of many aquatic animals such as fish.

- lead to sth ~ result in sth : dẫn tới cái gì

- die (v) chết - death (n) cái chết

`3,` Children are obliged to live with their parents until they reach the age of 18.

- be obliged to do sth : bị bắt buộc làm gì

`4,` She could go out until she finished her homework.

- until + HTĐ/ QKĐ : cho đến khi

- could do sth : có thể làm gì (trong quá khứ)

`5,` Because it rained heavily, we put off the picnic to the mountain.

- delay (v) trì hoãn ~ put off (phr v)