请教一个关于比较结构中的省略的问题，题目og16-35。

无情杀G

35. Traffic safety officials predict that drivers will be equally likely to exceed the proposed speed limit as the current one.
A. equally likely to exceed the proposed speed limit as
B. equally likely to exceed the proposed speed limit as they are
C. equally likely that they will exceed the proposed speed limit as
D. as likely that they will exceed the proposed speed limit as
E. as likely to exceed the proposed speed limit as they are
正确选E。
选E是没什么疑问的。但是想请教一下：E选项中如果把they are省略了会不会有错呢？
这个句子比较的对象是 the proposed speed limit 和 the current one，是不是只要把比较对象明确写出来就可以，其他相同的部分皆可省略？
E选项不省略they are 难道是因为时态和前面的they will be不同，所以不能省略吗？


求大神解答一下语法渣的疑惑啊( ⊙o⊙ )
这个问题升华一下就是，比较结构中什么是可以省略的，什么是不能省略的，什么是必须省略的，什么是省不省略都可以的？
或者各位大神有看过关于这个问题比较好的总结求推荐~
万分感谢！！！