Каждое предложение образовать в 3 условных типа 1) if you (to be) busy, i (to leave) you alone. 2) if my friend (to come) to see me, i (to be) very glad. 3) if he (to send)an e-mail, we (not toworry).

1If you are busy I'll leave you alone.
If you were busy I would leave you alone.
If you had been busy I would have left you alone.
2If my friend comes to see me I will (shall)be very glad.
If my friend came to see me I would be very glad.
If my friend had come to see me I would have been very glad.
3If he sends an e-mail we won't(shan't) worry.
If he sent an e-mail we wouldn't worry.
If he had sent an e-mail we wouldn't have worried.