$\text{7.}$

Vietnamese students have to wear uniforms when they go to school

- have to = obligate : phải/bắt buộc

(obligate mang nghĩa mạnh hơn)

$\text{8.}$

You musn't use your mobile phone on the plane

- musn't = not allow : nghiêm cấm/ không được phép (theo luật)

$\text{9.}$

If people use a lot of vehicles, the air will be polluted

- câu đk loại 1: If S + V(hiện tại đơn), S + will + V

$\text{10.}$

It has been 2 months since the last time he had his hair cut

- S + V (hiện tại hoàn thành) since S + V (quá khứ) : kể từ khi

$\text{11.}$

Despite being a developed country, Singarpore is not polluted by industry

- In spite of/ Despite + Noun/Ving : mặc dù 

$\text{12.}$

Both New Zealand and Australia has sea around it

- be surrounded by: được bao bọc bởi

- both A and B: cả hai