1 If mother buys a cake, we will have a very nice tea party.
If mother bought a cake, we would have a very nice tea party.
If mother had bought a cake, we would have had a very nice tea party.
2 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.
3 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 the exam.
4 If I live in Moscow, I will visit the Tretyakov Gallery every year.
If I lived in Moscow, I would visit the Tretyakov Gallery every year.
If I had lived in Moscow, I would have visited the Tretyakov Gallery every year.