China made a commitment to the world in the Copenhagen Summit that by 2020, the carbon-intensity of its economy ______ fall 40% to 45%.
| A．shall | B．may | C．must | D．should |
_____ of their bad habits, the boys switched from being dependent on their parents to _____ for others.
| A．Having rid; sacrificing | B．To rid; sacrifice |
| C．Rid; sacrificing | D．Having been rid; sacrifice |
Happy birthday, Alice! So you have _____ twenty-one already.
| A．become | B．turned | C．grown | D．passed |
The computer was used in teaching. As a result, not only _____, but students became more interested in the lessons.
| A．saved was teachers’ energy |
| B．was teachers’ energy saved |
| C．teachers’ energy was saved |
| D．was saved teachers’ energy |
Teachers have to constantly update their knowledge in order to maintain their professional(专业的)_______.
| A．consequence | B．independence | C．competence | D．intelligence |
Everything comes with _____ price; there is no such _____ thing as a free lunch in the world.
| A．a; a | B．the; / | C．the; a | D．a; / |