21. Young people are sharing more information aboutthemselves on social media sites now than they __in the past.
A)was C)do
B)are D)did
答案：D 表示过去时态，主语为复数故舍弃A，选D
22. One of thetoughest jobs of managers and executives is _____ how to engage theiremployees.
A)to figure out C)figure out
B)to be figuring out D)figuredout
答案：A， is 后面不能加动词原形，D表示被动语态，不符合，B表示进行时，不符合
23. _____ they are invented to be very smart, robots still can’t replacehumans.
A)If only 要是..就好了，表示虚拟 C)As if 好像
B)Even though 即使 D)Just as就像
答案：B
24. Thispassport photo doesn’t look like you at all, so you must have another one_____.
A)taking C)taken
B)to take D)took
答案：C， have sth done 的用法
25. We arepleased to share the news _____ we have finished our project ahead of schedule.
A)that C)those
B)which D)these
答案：A，该句子为同位语从句，_____ we have finished our project ahead of schedule是做news的同位语，that只是链接作用，不担当句子成分
26. The search will go on _____ a new and better material is found to replacethis one.
A)since 自从 C)while当…时候
B)until 直到 D)as 当..时候
答案：B
27. These photosremind me of the days _____ I stayed in Britain, working as a visitor scholar.
A)where C)whether
B)when D)how
答案：B，该句为定语从句，先行词为days表示时间
28. This websitemay contain links to other websites _____ privacy practices may be differentfrom ours.
A)that C)who
B)which D)whose
答案：D，定语从句，先行词为websites,后面的privacypractices与先行词构成从属关系
29. The company _____ its sales by an average of 10% per year since itsestablishment in 1993.
A)increases C)is increasing
B)increased D)has increased
答案：A，per year为关键，表示每年，公司每年的销售以10%增长，表示陈述事实，用一般现在时
30. The flight scheduled _____ at 9 a.m. was delayed four hours due to the badweather.
A)to take off C)taking off
B)take off D)to be taken off
答案：A,首先确定句子谓语是was delayed, 所以scheduled是非谓语成分，其完整表达是Be scheduled to do sth表示计划做某事，又因为take off 飞机起飞是不及物动词，无被动语态