1. If you (to be busy), I (to leave) you alone.
- If you are busy, I'll leave you alone.
- If you were busy, I'd leave you alone.
- If you had been busy, I'd have left you alone.

2. If I (to get) a ticket, I (to go) to the Philharmonic.
- If I get a ticket, I'll go to...
- If I got...,I'd go to...
- If I had got...,I'd have gone to...

3. If we (to receive) a telegram from him, we (not to worry).
- If we receive a telegram from him, we shan't worry.
- If we received....we shouldn't worry...
- If we had received...,we shouldn't have worried...

4. If he (to live) in Moscow, he (to visit) the Tretyakov Gallery every year.
- If he lives in Moscow, he will visit the Tretyakov Gallery every year.
- If he lived....he would visit...
- If he had lived ...he would have visited....