1. Mai's mother, who lives in Nha Trang, has 5 grandchildren.

N (người) + who + V 

2. The museum will be visited by millions of people.

S + will be + V3/ed: bị động - TLĐ

3. I avoid staying up late because it's not good for my health.

avoid + Ving: tránh 

4. If you don't save some money, you won't be able to buy the house.

if 1: If + HTĐ, S + will/can/shall .. + V1 

`color{orange}{~MiaMB~}`