Carbon dioxide from burning fuels is the most common of the so – called greenhouse gases．
| A．producing | B．having been produced |
| C．to be produced | D．produced |
You've ______ a zero in this phone number, so you can't get through.
| A．left out | B．broken out |
| C．put out | D．got out |
He did not regret saying what he did but felt that he ______ it differently.
| A．could express | B．would express |
| C．could have expressed | D．must have expressed |
--You didn't wait for Tom yesterday.
--Yes, but we ______. He didn't come.
| A．needn't have | B．didn't need to |
| C．could have | D．should have |
Sarah pretended to be cheerful,_________ nothing about the argument.
| A．said | B．to say | C．saying | D．to be saying |
Reportedly, the number of students _______ to computer games _____ been on the increase in recent years, which is a major concern for many people.
| A．devoted; has | B．related; have |
| C．connected; have | D．addicted; has |