求教关于省略的一题目！

39. A president entering the final two years of a second term is likely to be at a severe disadvantage and is often unable to carry out a legislative program.

A. likely to be at a severe disadvantage and is often unable to

B. likely severely disadvantaged and often unable to

C. liable to e severely disadvantaged and can not often

D. liable that he or she is at a severe disadvantage and can not often

E. at a severe disadvantage, often likely to be unable that he or she can

答案是A，但是我不知道为什么likely to be at a severe disadvantage and （is） often unable to。 括号里的is为什么不能省略呢？既然前面已经有is 了，is  likely to be at a severe disadvantage。

请大家帮助解释一下罗，谢谢拉！

如果省略 is 的话,有可能会产生两种不同句子结构,以至引起歧义:

1. is likely to be at a severe disadvantage and (is) often unable to

OR

2. is likely to be at a severe disadvantage and (be) often unable to