Ответ:

2. If my friend gave me a present that I didn't like, I'd keep it and say nothing

3. If I could speak perfect English, I'd become an interpreter

4. If I knew that a classmate was cheating in the exam, I'd talk to the classmate about it

5. If I broke my friend's mobile, I'd give him/her my mobile

6. If I found €100 in school, I'd give it to a teacher

The third conditions

Третий тип условных предложений

Имеет такую форму построения: Past Simple (придаточная часть; та, которая начинается с if/when) + would+Vинф.(главная часть)