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 wieght quicker than do
(B) associated with other calves, they require less medication and gain weight quicker than
(C) associate with toher 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 wieght more quickly than do
(E) associate with other calves, they require less medication and gain wight more quickly than

The correct answer is E and the explanation is: the first and last verbs in the series of verbs that describe the calves are in the present tense, so the tow in the middle should be as well: the calves exercise... associates... require... gain weight.

However the Manhattan GMAT prep for Sentence correction in Chapter 3, page 48 states that there are only 3 possibilities for the if-then clause, and that the "then" clause requires will+base verb, would/could+base verb OR would/could+have+past participle. The correct option does not follow any of these 3 structures.

How come there is a 4th option that according to the OG is correct. Can somebody please explain.

Thanks,

The difference one of meaning. If you use one of the WILL/WOULD constructions, you're usually implying some sort of remote or future consequence of the 'if' part. For instance: 'If you brandish a gun while committing a crime, you will be sentenced to at least ten years in prison.' Notice that the 'will' part - the prison sentence - is a consequence that comes after the given hypothetical (brandishing a gun), and is not contemporaneous with it.

If the 'then' condition is contemporaneous with the 'if' condition, you don't need to include the auxiliary verb - and, in fact, you'll usually be wrong in doing so.
Example: 'If a bacterium has chloroplasts, then it can make food from sunlight.' This sentence doesn't make sense with 'will be able to make food'.

I'll look at the strategy guide.

How cute - there's an (unintentional) example embedded in my own post: If you use one of the WILL/WOULD constructions, you're usually implying some sort of remote or future consequence of the 'if' part.

Again, note that the two parts - (1) using the construction, and (2) implying remote causation - are contemporaneous (you're implying remote causation WHILE you're writing the construction). This sentence wouldn't make sense if it were written '...you will imply...' or '...will be implying...'

In this 4th possibility, you are often giving a general rule using present tense in both the IF clause and the THEN clause:

"If I eat pizza, [then] I feel bloated."

In this case, "If" is basically equivalent to "Whenever":

"Whenever I eat pizza, I feel bloated."

To be fair, the Strategy Guide section is talking about *hypothetical* conditions constructed with "if/then," but we should clarify the point and add this 4th non-hypothetical construction to the list of if/then possibilities. We'll do so in the next edition. Thanks for flagging the issue!