1.Lan will ask her teacher.He will explain it to her
=>If Lan asks her teacher, he will explain it to her
2.We don't have holiday because we haven't got any money
=>If we got money, we would have holiday
3.we will have holiday.we will go to Thailand
=>if we have holiday, we will go to Thailand
4.drive carefully or you'll have an accident
=>if you don't drive carefully, you'll have an accident
5.Lan's parente don't live near.Hanoi,so she doesn't see them on weekend
=>if Lan's parents lived near Hanoi, she would see them on weekend
6.i don't know the answer so i ean't tell you
=>if I knew the answer, I would tell you