Carbon dioxide(CO2)_______ 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 |
To everybody’s surprise ，the fashionable young lady_________to be a thief。
| A．found out | B．proved out | C．put out | D．turned out |
Collecting stamps as a hobby ________increasingly popular during the past fifty years。
| A．becomes | B．became | C．has become | D．had become |
Jack had____________feeling of excitement when hearing his article had been published in ______school magzine。
| A．the ；a | B．a ；the | C．/ ；the | D．the ；/ |
Bill ______ a couch potato and now he has a healthy lifestyle.
| A．is | B．used to be | C．is used to being | D．is used to be |
After many failures the most difficult ______ is how to keep our strength up and fight again.
| A．chance | B．change | C．challenge | D．challenger |