Поставьте либо в условное предложение 1 либо 2 типа 1) if the train (be) late, we won't be able to see them. 2) if you study hard, you (pass) your exam.

1) If the train is late, we won't be able to see them.
2) If you study hard, you will pass the exam.
Использован first conditional (1-ый тип)