prep p1-142.

According to a 1996 study published in the Journal of Human Resources, Americans of Middle Eastern descent were twice as likely as was the national average to be self-employed.

(A) as was the national average to be self-employed

(B) as the average American to be self-employed

(C) as the national average that they would be self-employed

(D) to be self-employed than was the average American

(E) that they would be self-employed than was the national average

答案:B  这个为什么不把was补出呢?

只有在不补可能存在歧义的时候才补，NATIONAL AVERAGE 前面只有 主系 结构， 一看就是主语跟主语比较， 补出来就显得多余。

其实即使 是S。V。O THAN 结构 也有不补助动词的时候， 判断关键在于有无合理的歧义。