At times the balance in nature is ______, resulting in a number of possibly unforeseen effects.
| A．confused |
| B．puzzled |
| C．disturbed |
| D．troubled |
Isn't it time you got down tothe papers?
| A．mark | B．be marked | C．being marked | D．marking |
I just wonder ____ that makes him so excited.
| A．why it does | B．what he does | C．how it is | D．what it is |
Some people fear that ________ air pollution may bring about changes in _______ weather around the world.
| A．/; the | B．the; / | C．an; the | D．the; a |
The doctor must be _______ 24 hours a day, 7 days a week in the boarding school.
| A．on call | B．by hand | C．in sight | D．on spot |
What was considered impolite years ago has become ________now.
| A．accessible | B．adjustable | C．unbelievable | D．acceptable |