1. If he came on time, this might not have happened.
2. It is a pity that you will be so busy in the evening and cannot help me.
3. What would you do if a building started a fire?
4. If not for his work, he would be able to become your guide in St. Petersburg with pleasure.
5. I do not like skiing, otherwise I am. perhaps the countryside would have traveled with you on such a wonderful winter day.
6. It is a pity that you then did not understand how wrong you were.
7. You won’t understand anything if you don’t listen to me carefully.
8. If I knew that you were at home last night, I would have rushed to you for a moment to chat and have a cup of tea.
9. If he had been even a little wiser, he would not have squandered his entire fortune by gambling.
10. I did not blame him. In his place, I would do the same.
B.
1. He must know this.
2. He must know this.
3. He probably knows that.
4. He can easily find out.
5. He may know this.
6. He may know this, only I do not believe in it.
7. Does he really know that?
8. It cannot be that he knows this.
9. He should not know this, this is classified information.
10. He should not know this.
11. He could have found out about it himself.
12. He has to find out. about everything myself.
13. You do not need to know about this, I will figure it out myself.
14. He was soon to learn about it.
15. He must know this.
In conclusion I'd like to add that there're many ways to learn English. I want to try them all.