下列短文中有十個(gè)空白，每個(gè)空白有四個(gè)選項(xiàng)。根據(jù)上下文要求選出最佳答案，并在答題紙上將相應(yīng)的字母涂黑。

　　The basic principle of radar is illustrated by what happens when one shouts in a cave. The echo of the shouting 11 the walls helps a person determine the size of the cave. With radar, however, the waves are radio waves instead of 12 _ waves. Radio waves travel 13 the speed of light, about 300,000 kilometers in a second. A radar set _ 14 _ a short burst of radio waves. Then it receives the echoes _ 15 when the waves bounce (反射) off objects. By determining the time it 16 for the echoes to return to the radar set, a trained technician 17 determine the distance between the radar set and other objects. The word '6radar", 18 , gets its name from the term "radio detection and ranging." "Ranging" is the term for detection of the 19 between an object and the radar set.

　　Besides being of critical importance to pilot, radar is 20 for air traffic control, for tracking ships at sea, and for tracking weather systems and storms.

　　11. A. through B. for C. on D. agamsr

　　12.A.sound B. light C. heat D. tide

　　13.A.in B. at C. over D. on

　　14. A. sends out B. works out C. figures out D. puts out

　　15. A. producing B. produced C. produce D. produces

　　16.A. spends B. takes C. kills D. makes

　　17.A.can B. must C. ought to D. has to

　　18.A.in case B. in turn C. in short D. in fact

　　19.A.length B. width C. distance D. space

　　20. A. eventual B. internal C. external D. essential

　　相關(guān)推薦：

　　2014自考《政治經(jīng)濟(jì)學(xué)(財(cái))》考前鞏固練習(xí)題匯總

　　2014年自學(xué)考試：練習(xí)3小時(shí)搞定政治公共課

　　2014年10月自考得高分的四種答卷策略

　　2014年自學(xué)考試《大學(xué)語(yǔ)文》備考秘籍