Question

[ngọc linh]

They don't feel healthy because the air isn't pure
->if 
It wasn't fine yesterday so we didn't have a picnic
->If
Because my uncle was poor, he couldn't buy that house
->If
 

Answer 1

[Dang Khoa ~xh]

If the air is pure, they will be healthy.

If it had been fine yesterday, we would have had a picnic. 

If my uncle wasn't poor, he could buy that house