1. My mother cooked a meal yesterday. It was very delicious. (Dùng đại từ quan hệ)
The meal , which my mother cooked a meal yesterday , was delicious 
2. He says he will help me, but I don’t believe him.
Although he says he'll help me , i don't believe him.
3. Save electricity, or else you will pay much per month. ( câu điều kiện loại I)
You won’t pay much per month , you  save electricity
4. Let’s meet inside the center, at the cafe’s corner.
I suggest insiding the center , at the cafe's corner
5. Why don’t you plant some trees around your house to get more fresh air?
How about planting some trees around your house to get more fresh air
6. “What about changing the date of the meeting again?” Mr. Nick said.
Mr. Nick suggested changing the date of the meeting again
7. It has started to rain, so stop playing tennis.
We stopped playing tennis because it's has started to rain