17.I have never met a famous person before
It is the first time I've met such a famous person.
18. The sun is much hotter than the moon.
The moon isn't as hot as the sun.
19. You can't read more quickly than i can.
I can not read as slowly as you.
20. Thank you for helping me
It was kind of you to help me.
21. You can't understand these things because you are very young.
You are not old enough to understand these things.
23. The last time i saw Lan was at Tam's birthday party.
I haven't seen Lan since Tam's birthday party.
24. Where is the dentist's office?
Could you tell me the way to the dentist's office?
25.This shirt is too dirty for me to wear.
This shirt isn’t clean enough for me to wear.