21. ---I bought the coat for 270 yuan last week.
---It’s on sale today 200yuan. You should have waited.
---Oh ,really? But how _____I know?
A. would B. do C. can D. did
22. ----Shall I give you a ride as you live so far away?
----Thank you. _______.
A. It couldn’t be better B. Of course you shall
C. If you like D. It’s up to you
