17. Chemistry is les interesting than physics.
Physics is more interesting than chemistry.
18. John can't type as quickly as Peter.
Peter can type more quickly than John.
19. My brother is tall but you are taller.
My brother is not as tall as you.
20. Dogs are friendlier than cats.
Cats aren't as friendly as dogs.
21. Linda sang more beautifully than her friend.
Her friend didn't sing as beautifully as Linda.

17. Physics is more interesting than chemistry.
18. Peter types more quickly than John.
19. My brother is tall, but you are taller.
20. Cats aren't as friendly as dogs.
21. Linda's friend didn't sing as beautifully as Linda did.