21. It's quite ____ me why such things have been allowed to happen.
A. for B. behind C. against D. beyond
22. --Some people believe that robots will take over the world one day.
--What if that is the ______?
A. thing B. condition C. case D. end
23. Smith was overweight, so the doctor urged that not only ____ have less fat and meat, but also he ______.
A. should he; take exercise B. must he; take exercises
C. he can; does some exercises D. he ought to; do some practice
