Сделайте по примеру: If you (to be) free,I (to come) to see you.
1) If you are free,I shall come to see you
2)If you were free,I should come to see you
3)If you had been free,I should have come to see you

1.If mother (to buy) a cake, we (to have) a very nice tea party
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2.If we (to receive) a telegram from him,we (not to worry)
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3.If you (not to work) hard,you (to fail) the exam
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 If my mother would  buy a cake, we will have a good tea party.If my mother bought a cake, we would have a good tea party.If my mother had been bought a cake we would have a good tea party