Давайте разберём ваши примеры и заполним необходимыми формами глаголов. Я представлю три типа предложений, соответствующие условному предложению.
If you are busy, I shall not come to see my friend.
- If you were busy, I should not come to see my friend.
- If you had been busy, I should not have come to see my friend.
If mother buys a cake, we shall have a very nice tea party.
- If mother bought a cake, we should have a very nice tea party.
- If mother had bought a cake, we should have had a very nice tea party.
If he sends an e-mail, we shall not work systematically.
- If he sent an e-mail, we should not work systematically.
- If he had sent an e-mail, we should not have worked systematically.
If you do not pass the exam, you will fail.
- If you did not pass the exam, you would fail.
- If you had not passed the exam, you would have failed.
If I visit the Tretyakov Art Gallery, I shall get a ticket.
- If I visited the Tretyakov Art Gallery, I should get a ticket.
- If I had visited the Tretyakov Art Gallery, I should have gotten a ticket.
If you live in Moscow, I shall go to the Philharmonic.
- If you lived in Moscow, I should go to the Philharmonic.
- If you had lived in Moscow, I should have gone to the Philharmonic.
If I go early, we shall watch TV together.
- If I went early, we should watch TV together.
- If I had gone early, we should have watched TV together.
If she knows English, she will try to enter the university.
- If she knew English, she would try to enter the university.
- If she had known English, she would have tried to enter the university.
If my father returns, I shall be very glad.
- If my father returned, I should be very glad.
- If my father had returned, I should have been very glad.
If he left you alone, you would be happy.
- If he leaves you alone, you will be happy.
- If he had left you alone, you would have been happy.
Теперь все примеры представлены в трёх типах условных предложений. Если у вас есть дополнительные вопросы или нужны другие примеры, пожалуйста, дайте знать!