64. [Even though]Sedat [has been studying] English for three years before came to
     A                   B  
 [the United States] ,it is still difficult or him [to express himself.] 
C                                        D                          
答案：B 时态。学英语是发生在去美国之前，而句中去美国用的是过去式，所以应该用过去完成时，把B项改为had been studying。

65 .[A number of] foreign visitors [were taken] to the industrial exhibition [which] 
　　　A                      B                            C
they [saw] many new products. 
　　 D　　　   
答案：C 关联词。Which 引导的是一个定语从句，但先行词exhibition在句中是做地点状语，所以在which前应加一个on。

66. It is [driving] [on the left][ what] causes visitors to Britain the [most]
        A        B         C                        D
trouble.                                     
答案：C 强调句。it is…that 是强调句的固定结构，应把C改为that。　　　　　　　　　　

67. When she [came] back from Hollywood, she wanted [to tell] everybody
　　　　　A                                    B
[about] all the stars and exciting people [who] she had seen.              
C                           D
答案：D 关联词。Who 引导的是一个定语从句，但先行词在句中做的是宾语，所以应把who改为whom。

68. [Many] of the society's wealth is [controlled] by large [corporations] and
   A                         B                      C