27. B
present解释为“出席的,在场的”时,一般做后置定语；而解释为“现在的,目前的”时,做前置定语.
翻译：出席会议的人们都很担心目前的形势.
28. B
此处over是介词,可翻译为“一边...,与...同时”.
再如：We had a nice talk over a cup of coffee.
我们一边喝咖啡,一边愉快地交谈.
29. B
so/such...that...句型的倒装结构.前句部分倒装,后句不倒.
再如：So fast did he run that I didn't catch up with him.
30. D
只有as/which可以这样引导一个非限制性定语从句.as/which代替the Beatles, 做定语从句中remember的宾语.
31. C
固定句型：the same...as...；而比较是拿同等事物比较的,所以用what is learned through experience去等同于what is learned in books.