1 . We all need to get involved in saving energy ________ it's at work, at home, or at school.

A．unless

B．once

C．whether

D．because

2 . Henry David Thoreau was happy to ________ from social life, seeking a harmonious relationship with nature in the quietness of his life.

A．judge

B．differ

C．withdraw

D．benefit

4 . Of the nineteen recognized polar bear subpopulations, three are declining, six ________ (be) stable, one is increasing, and nine lack enough data.(所给词的适当形式填空）

5 . The Xi’an City Wall is the most complete city wall that has survived China’s long history. It ________ (build) originally to protect the city in the Tang Dynasty and has now been completely restored (修复).

6 . My bike was old and shaky ________ did the job.（用适当的词填空）

7 . It was the first time in six attempts that Peters ______the world champion.

A．has beaten	B．was beaten
C．beat	D．had beaten

8 . The ________ (beauty) long branches covered with pink-colored buds (蓓蕾) make fantastic decorations. （所给词的适当形式填空）

9 . After spending some time looking at all the defensive equipment at the wall, we decided it was time for some action and what ________ (good) than to ride on a piece of history!(所给词的适当形式填空）

10 . It ________ (build) originally to protect the city in the Tang dynasty and has now been completely restored (修复). (所给词的适当形式填空）