The amount of refrigeration and transport required to bring a food

You should always pay close attention to the specific boundaries around what's relevant, but on this type of problem it's even more important than usual to read the problem statement, and/or the conclusion of the argument, very carefully to learn EXACTLY what is relevant.

In this problem, you have to find both a strengthener and a weakener for the same conclusion—so don't hesitate to take extra time to confirm the boundaries around what's relevant to that conclusion.

The conclusion says:
To reduce carbon emissions associated with their food, consumers in our community should choose locally grown foods over organically grown foods

This conculsion puts two absolute boundaries around what's relevant here.  First, we're ONLY concerned with carbon emissions—so the "other harmful chemicals" mentioned in the passage are not relevant.  And second, the conclusion does not extend beyond consumers in the speaker's community—meaning that if we see anything about overall market averages, general statistics for the entire surrounding region, etc., those things can't speak more specifically to the specific situation of this one community.


Now for the answer choices.


A/
This is an overall average for some larger region that's broader than the community in which we're actually interested, so we know right away that we won't be able to do anything useful with this statistic.  (No need to bother analyzing what it may or may not tell us.)

B/
The information in the passage tells us that the transportation of organic foods, which covers substantially longer distances, releases more carbon emissions—the single pollutant we actually DO care about—than does the shorter-distance transportation of foods grown closer to home.  
But if choice B is true, then we have another differential in carbon emissions to consider—this one going in the opposite direction of the differential in transport-related emissions.  The information in this choice, therefore, helps to neutralize the original inequality in carbon emissions; at a minimum, the magnitude of that inequality is reduced by the information in choice B.  So this is the choice that WEAKENS the original argument.

C/
The food described in this answer choice is NEITHER organically grown NOR local to the community where it's eaten (since it's transported from the farm to somewhere far away).  The comparison in the argument only involves two types of food: /1/ organically grown food that comes from farther away, and /2/ non-organic food grown closer to the community itself.  Since the food in choice C is not either of these, it's irrelevant to the comparison and therefore to the argument as a whole.
(The other problem with choice C is that it we're told only that this fact is "often" true; there's no way to know whether the single community in which we're actually interested constitutes one of the cases where this happens.)

D/
The statement in the original passage about the transportation of organic food over long distances suffers from the same weak wording just described at the end of choice C: Organic food is "often" transported over long distances, but there's no way to know for sure whether that's actually true in the single community we're talking about.
This is the gap that choice D fills, by saying that almost none of the organic food that's available for purchase in THIS community is actually grown locally—thus confirming that the organic food sold in THIS community has been trucked in from far away.  By reinforcing that weakly worded statement, this choice STRENGTHENS the original argument.

E/
The current argument is only about comparative amounts of carbon emissions.  We do not care about any other chemicals or other pollutants.