~Ответ
1. 1) Every time he came to visit me in Warsaw my friends used to give a party.
2) If my friend visited me in Warsaw, my friends would give a party.
2. Susan used to never talk about her friends behind their backs when she wa a student.
3.
1) They used to have many friends in their hometown but now in London they feel very lonely.
2) If they had many friends in London, as they had in their hometown, they would not feel very lonely.