1.Johnson had made up his mind to give it up, but on ________ second thought he determined to try ________ third time.
A. /; a B. the; /
C. a; a D. the; a
【答案】A
【解析】
【详解】考查冠词。第一空on second though是固定短语，意为“三思，再三考虑”；第二空序数词前用不定冠词表示“再一，又一”。句意：约翰逊已经下定决心放弃了，但是思虑再三后，他决定再试一次。故A选项正确。
2.If you really have to leave during the meeting, you’d better leave ____ the back door.
A. for B. by C. across D. out
【答案】B
【解析】
【详解】考查介词辨析。句意：如果你真的必须在会议期间离开，你最好通过后门离开。介词by表示“通过”，for 表示“目的”，across 表示“横穿”，out 表示“在外面”。开会期间离开最后通过后门离开。故选B。
3.— Look! Sam is running so fast!
— Hard to _________ his legs were once broken.
A. find B. know C. realize D. imagine
【答案】D
【解析】
【详解】考查动词词义辨析。句意：—你看！Sam跑得真快呀！—很难想象他的腿从前断过。A. find发现；B. know知道；C. realize意识到；D. imagine想象。根据Look! Sam is running so fast!可知，D项符合题意。故选D项。
