17. I prefer video games to computer games
18. my mother prefers cooking to cleaning
19.my friend like doing aerobics than swimming

17. I like video games better than computer games.

I prefer.......... video games to computer games 

18. My mother likes cooking better than cleaning.

My mother prefers....... cooking to cleaning

19. My friend prefers doing aerobics to swimming.

My friend likes.. doing aerobics better than swimming