OG和白勇上面的比较形式的省略问题

wyx19911103

OG verbal 第38题。A study commissioned by the Department of Agriculture showed that if calves exercise and associate with other calves,they require less medication and gain weight more quickly than those raised in confinement.为什么than后面不用加do?

白勇200页第30题 The US government employs a much larger proportion of women in trade negotiations than does any other government.
为什么这里又要加does?两题有什么区别么

soulwangh

If there is no ambiguity, you don't need to use a helping verb.

In the first sentence, those refers to calves, and you can see clearly that the compared objects are different kinds of calves rather than weight and calves raised in confinement.

In the second sentence, without the helping verb, it is possible to interpret the sentence as making a comparison between women and any other government, a interpretation distorting the intended meaning.