Scientists have made genetic modifications to cotton to increase its resistance to insect pests. According to farmers’

What we see: a Critical Reasoning "evaluate the argument" question. We need the fact that would most change how strong the conclusion is.

Step 1. Find the conclusion and the evidence.
What we see: the conclusion is that switching to the modified seed would not help most cotton farmers make more money. The evidence is that farmers who tried the modified seed used only slightly less insecticide per acre than farmers who did not.
What it means: the whole argument rests on one comparison between two groups of farmers: the ones who tried the seed and the ones who did not.
What we do and why: we ask whether those two groups were alike before the seed. If they were not, the comparison tells us little about what the seed does.

Step 2. Find the hidden assumption.
What we see: the argument treats "slightly less insecticide than the other group" as "the seed saves only a little insecticide."
What it means: that only works if both groups would have needed about the same amount of insecticide without the seed.
What we do and why: we look for a choice that tests that assumption, because that is the fact that could make or break the argument.

Step 3. Go through the choices.
A. Other genetically modified crops these farmers grew say nothing about cotton insecticide or cost. Out.
B. Comparing cotton insecticide prices with other crops' prices does not tell us whether the modified seed saves cotton farmers money. Out.
C. Whether cotton is a farmer's main crop does not change whether the seed pays for itself per acre. Out.
D. Total acres planted does not matter, because the evidence is already per acre. Out.
The right choice asks whether the farmers who tried the seed did so because they used to need exceptionally large amounts of insecticide. If yes, those farmers started far above everyone else, and getting down to only slightly less than normal farmers means the seed cut their insecticide a lot. Then the seed may save real money and the argument falls apart. If no, the groups were alike and the argument stands. Either answer changes our judgment, so this is the fact to know.

The trap: D looks like it checks whether the groups are alike, but acres do not matter when the numbers are already per acre.
Takeaway: When an argument compares people who chose something with people who did not, ask whether the two groups were different before the choice.

Answer: E