1. They can't answer these questions.

I wish they could answer these questions.

2. "Why don't you go out to get more fresh air?", he said to me

=> He suggests that I go out to get more fresh air.

3. Lan is very lazy, so she can't pass the English exam.

=> If Lan weren't so lazy, she could pass the English exam.

4. We started to learn how to swim in 2018.

=> We have been learning how to swim since 2018.

5. Nga doesn't have much money but she can buy a new car.

=> Although Nga doesn't have much money, she can still buy a new car.