50. We were young men [when] we [first met] in London, poor, [struggle], [full of]
                     A          B               C          D
hope and ideas.                   
[答案] C并列结构。

51. Of the two lectures, [the first] was by far [the best on], partly because the person
A                 B  
who delivered [it] had [such] a pleasant voice.
          C           D

[答案] B  代替。

52. [According to] our estimate, only one [out of] three company managers [have been]
        A                         B                        C
trained in the [field of] management.
        D                                                               
[答案] C 主谓一致。

53. Today we [have mad] [great achievements], but tomorrow we [shall win]
               A           B                     C    
still [great victories].
          D
[答案] D比较级。

54. Lewis had to travel by bus [as] his car [had been damaged] in an
                         A                B
 accident some days [before] and he [was failed] to get it repaired.
                    C              D
[答案] D 被动时态。

55. [Collecting] toy cars as a hobby [becomes] [increasingly] popular during the [past]
      A                          B        C                  D