1 If we receive a telegram from him, we won't worry. If we received a telegram from him, we wouldn't worry. If we had received a telegram from him, we wouldn't have worried. 2 If you don't work systematically, you will fail the exam. If you didn't work systematically, you would fail the exam. If you hadn't worked systematically, you would have failed exam.3 If I live in London, I will visit Big Ben every month .If I lived in London, I would visit Big Ben every month. If I had lived in London, I would have visited Big Ben every month.4 If I get a ticket, I will go to the theater. If I got a ticket, I would go to the theater. I I had got a ticket, I would have gone to the theater.