19. We live day by day, but in the great things, the time of days and weeks ______ so small that a day is unimportant.

A. is                         B. are                       C. has been               D. have been

分析：A。句子主語(yǔ)為the time，故用謂語(yǔ)要用單數(shù); 再根據(jù)句子前后的時(shí)態(tài)live和is，可知此處宜用一般現(xiàn)在時(shí)，不用現(xiàn)在完成時(shí)，故選A。

20. — ______ you ______ him around the museum yet?

— Yes. We had a great time there.

A. Have; shown         B. Do; show              C. Had; shown          D. Did; show

分析：A。根據(jù)問(wèn)句中的yet可知，所談?wù)摰氖虑榘l(fā)生在最近的過(guò)去，且問(wèn)話者很關(guān)心這個(gè)過(guò)去發(fā)生的事情對(duì)現(xiàn)在的影響和結(jié)果，所以用現(xiàn)在完成時(shí)。注意：不要受答語(yǔ)中過(guò)去式謂語(yǔ)had的影響而誤選C。

21. —I have got a headache.

—No wonder. You ______ in front of that computer too long.

A. work                    B. are working          C. have been working    D. worked

分析：C。由于在電腦前工作太久，所以導(dǎo)致了現(xiàn)在頭痛的結(jié)果，故空格處應(yīng)填現(xiàn)在完成時(shí)或現(xiàn)在完成進(jìn)行時(shí)，即答案選C。

22. Professor James will give us a lecture on the Western culture, but when and where ______ yet.

A. hasn’t been decided                               B. haven’t decided    

C. isn’t being decided                                D. aren’t decided

分析：A。根據(jù)句意，此處應(yīng)用被動(dòng)語(yǔ)態(tài)，不用主動(dòng)語(yǔ)態(tài); 再根據(jù)句末的yet可知，最好用現(xiàn)在完成時(shí)。故選A最佳。

23. So far this year we ______ a fall in house prices by between 5 and 10 percent.

A. saw                      B. see                       C. had seen              D. have seen

分析：D。短語(yǔ)so far意為“到目前為止”，它習(xí)慣上要與現(xiàn)在完成時(shí)連用。

24. —Do you think we should accept that offer?

—Yes, we should, for we ______ such bad luck up till now, and time ______ out.

A. have had; is running                              B. had; is running     

C. have; has been run                                 D. have had; has been run

分析：A。根據(jù)句中的up till now可知，第一空應(yīng)填現(xiàn)在完成時(shí)，故可排除B和C；run out的意思是“（時(shí)間）流逝”，為不及物動(dòng)詞，以時(shí)間名詞作主語(yǔ)時(shí)，沒(méi)有被動(dòng)語(yǔ)態(tài)，故可排除D。

25. —Have you known Dr. Jackson for a long time?

—Yes, since she ______ the Chinese Society.

A. has joined             B. joins                     C. had joined            D. joined

分析：D。since she join the Chinese Society為I have known Dr. Jackson since she join the Chinese Society之省略。連詞since所搭配的時(shí)態(tài)通常是：主句用現(xiàn)在完成時(shí)，從句用一般過(guò)去時(shí)。