i actually agree with the original poster on this question -- choice (b) is the best of the available options.
here the reasoning:
both (b) and (d) involve correctly parallel constructions; the difference is solely rhetorical.
in other words, not only do both of those options have parallel elements, but they both invoke those parallel elements in ways that make sense.
the meanings are slightly different -- the version involving "to" indicates a sense of purpose, while the version involving "and" merely states that they are doing multiple things -- but either one of them could be legitimate. (note to test takers: this is one sign of a badly written problem -- you can't even tell what is the intended meaning!)
however, the answer indicated as correct is actually incorrect, since the comma that precedes the word "and" in that choice is straight-up WRONG.
remember that lists of two items connected by "and" do not contain commas, while lists of three or more such items must contain commas.
the problem, then, is that choice (d) actually contains a list of just two items. one of those items is a compound of three things, but, in the context of the larger list, it counts as a single item:
improving productivity means bringing techniques, equipment, and seeds up to global standards AND cultivating...
this is a list of only two items (namely, the items that are highlighted in red), so there absolutely should not be a comma before "and".
from what source is this question taken? i've seen a couple other problems taken from this source, and they have uniformly been awful, almost to the point where i question whether the authors have ever actually taken a look at the actual gmat.
Ron has been teaching various standardized tests for 20 years.
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