Ответ: 1. This is my friend.- These are my friends.
2. This is a nice melody. — These are nice melodies.
3. That is a tall man. — Those are tall men.
4. This is a nice day. — These are nice days.
5. That is a small mouse. — Those are small mice.
6. I was a sportsman. — We were sportsmen.
7. He is a boss. — They are bosses.
8. This is her child. — These are her children.
9. That was a bus-stop. — Those were bus-stops.
10. I am a lady and he is a gentleman. — We are ladies and they are gentlemen.