OG if......they will do.....和 if....... they do

A study commissioned by the Department of Agricul­ture showed that if calves exercise and associated with other calves, they will require less medication and gain weight quicker than do those raised in confinement.

(A)  associated with other calves, they will require less medication and gain weight quicker than do

(B)  associated with other calves, they require less medication and gain weight quicker than

(C)  associate with other calves, they required less medication and will gain weight quicker than do

(D)  associate with other calves, they have required less medication and will gain weight more quickly than do

(E)   associate with other calves, they require less medication and gain weight more quickly than

if……, they will我觉得是固定搭配……if的will被改成了一般现在时……

为什么E没有will？？

谢谢…………

表示客观事实.