OG46-比较句中助动词何时需补齐

各位大虾，有关OG46的两个语法点不清楚，可否帮忙解释，谢谢！

46. 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.

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

1。为什么“require"及“gain"不用将来时，不是应该“X will happen if y happens(OG37)"

2。为什么”than"后不用补齐助动词"do"，但在OG12及OG19中都补齐了？

可否告之何种情况下需补齐助动词。

1.  ' A study showed '  So this has been proven, therefore it is a fact.  And for facts, we use present tense.

2. 'Do' should be placed after 'than those reaised in confinement' (do)

'Do' should be placed after 'than those reaised in confinement' (do)

If "do " can be ommitted ,why is the answer E of OG19 wrong?

"19. In addition to having more protein -than wheat does, the protein in rice is higher quality than that in wheat, with more of the amino acids essential to the human diet.

E rice has a protein higher in quality than

同样的问题.第一个解释还说得通,第二个比较牵强,难道只能说劣中选优?

you guys can refer to this thread

http://forum.chasedream.com/dispbbs.asp?BoardID=23&replyID=983810&id=103101&skin=0

it's the best...

真怀疑楼上的是不是把所有的帖子都背下来了。。。