In recent years cattle breeders have increasingly used crossbreeding, in part that their steers should acquire certain characteristics and partly because crossbreeding is said to provide hybrid vigor.

(D) partly beacuse certain characteristics should be acquired by their steers

(E) partly to acquire certain characteristics in their steers

这题我做了好几遍了，没一次都错， 每一次都选D， 因为前后对称，情态动词 should不可以随便省略， 并且我也不觉得“牛应该获得一些特征”有什么逻辑得错误，所以每次都错。大家都是怎么做得呢？哪位大侠可以教教我！！！

这道题目的确需要考虑平行结构,但是
在考虑平行前,
1)需要和主句配合起来
use sth to do 是这里首先需要考虑得,目的都用TO DO

2)再考虑平行结构,

D是个迷惑选项,ETS常用这样的选项来迷惑咱们

就象either ... or 等的平行结构里,喜欢用ing这样的名词,
然后选项里再加上ING形式的结构.