怎么做这几道题目

11. The beam that is ________by a laser differs in several ways from the light that comes out of a flashlight.

A) emitted C ) motivated

B) transportedD) translated

12. We booked rooms at the hotel ________we should find no vacancies on our arrival.

A) wheneverC) since

B) if D) lest

13. Modern forms of transportation and communication have done much to ________the isolation of life in Alaska.

A) break throughC) break into

B) break downD) break out

14. We know through painful experience that freedom is never by the oppressor; it must be ________by the oppressed.

A) demandedC) required

B) commanded D) requested

15. Color and sex are not relevant ________whether a person is suitable for the job.

A) on C) to

B) for D) with

12题应该选 D . "lest"有”以免；以防”的意思，后面接 should+动词原形．如果选 C 的话 should 不符合语法规则．