23. As more and more nations put satellites into space, the risk of ________ can only increase as a result.

　 A. collision　 　　B. discovery　　　 C. crash　　　　 D. invention

22. As economy was declining, jobs _________to the laid-off workers continued to be scarce.

　 A. valuable　　　 B. convenient　　　 C. comfortable　　 D. available

　第一节: 多项选择 (共10小题; 每小题1分,满分10分)

21. The captain showed great perseverance and never __________ to disappointment, even when the ship sank.

　 A. gave off　　　 B. gave away　　 C. gave way　　　 D. gave up