OG11紫色39 请教

39. 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

Verb form + Diction

The first and last verbs in the series of verbs that describe the calves are in the present tense, so the two in the middle should be as well：the Calves exercise．．．associate．．．require．．．gain weight．

这题根据平行选E是没说的。但OG解释中关于动词形式（highlight部分）我不明白。不是说如果条件状语从句是一般现在时，主句是将来时吗？这题里面主、从都是一般现在时呀，可以这样吗？请明白人指点。谢谢！