求解prep08中一个关于对比题中省略的问题

哈雷扫把

Today's techonology allows manufacturers to make small cars more fuel efficient now than at any time in their production history.

a. Same as above
b. small cars that are more fuel-efficient than they were at any time in their
c. small cars that are more fuel-efficient than those at any other time in
d. more fuel-efficient small cars than those at any other time in their
e. more fuel-efficient small cars now than at any time in
这道题的答案是C

Soaring television costs accounted for more than half the spending in the presidential campaign of 1992, a greater proportion than it was in any previous election.
A.    a greater proportion than it was
B.    a greater proportion than
C.    a greater proportion than they have been
D.    which is greater than was so      
E.    which is greater than it has been
这道题的答案是B
为什么第二道题的正确答案可以省略掉proportion，than后面直接跟介词短语，而第一道题不可以呢？单独看的时候我都没有问题，可是两道题放在一起我发现我很困惑，求指教

rabbit1937

当然这道题目可以有很多方法排除，比如说A中的today与now重复；各种in any time（也包括现在）错误。

就比较部分的语法来说，A和B我认为都没有错。但是不同结构下面，比较的含义就发生了改变，或者发生了歧义。

例如B中，they指代前面的car，就有问题了。A中的问题更多，at any time到底是说谁，和谁的时间比，technology？car？过去的还是新的car？搞不清楚