Before 1986 physicists believed they could describe

Okay, let's take this baby down. Here is the full "GMAT Jujitsu" for this question:

First, we need to recognize the problem type. This is a Strengthen question, as evidenced by the phrase, “which of the following…most strengthens the argument.” Our first item of business is to identify the conclusion of the argument and then look for gaps between the conclusion and the premises. However, here the GMAT throws a small curveball at us. Question stems given in problems often contain much more than just clues to the problem’s type. The conclusion in this argument is actually embedded in the question stem: “there is a fifth universal force.” The link between this conclusion and the evidence is tenuous, based off of the interpretation of data in a set of experiments, whose results merely imply the possibility of an additional force heretofore unknown. We must look for an answer that strengthens this logical link.

Answer choice “A” is completely irrelevant to the logical gap. Think about the conclusion we want to strengthen: "there is a fifth universal force." The majority of the problem focuses on the experimental evidence accrued after 1986. Whether scientists had sophisticated equipment prior to the 1970’s sheds no additional light on the existence of a fifth universal force. While scientists may not have had the technology before the 1970s to detect the small perturbations measured in the 1986 experiments, the existence (or lack) of equipment that could measure the force doesn't do anything to prove (or disprove) the conclusion. It is the data discovered by the equipment that matters. When the equipment was invented is mere context. This one is easy to eliminate.

The Testmaker intentionally disguised answer choice “B” with a double negative. This is classic trap of the GMAT. I call it "Convoluted Camouflage" in my classes. Rephrasing this answer choice by cancelling out the double negative may make the statement easier to understand: instead of saying, “no previously established scientific results are incompatible with the notion of a fifth universal force,” we could say, “previously established scientific results are compatible with the notion of a fifth universal force.” While this is a very weak statement – it demonstrates the lack of disconfirming evidence more than it provides new evidence – this is the only answer that nudges us in the right direction. Remember: “Strengthen” questions are not “Prove” questions – we are looking for the answer that “most strengthens” the existing argument.

Another way to think about the question of whether a statement is required by an argument is to think about what happens to that argument if the assumption turns out to be false. If the argument cannot possibly succeed when the assumption in an answer choice were false, then the original answer choice is an assumption required by the argument. This is the fundamental idea behind a strategy I call the "Assumption Negation Technique", which we can also apply to answer choice “B”. If we were to logically negate answer choice “B”, it would tell us that there were some "experimental results incompatible with a fifth force." This negation directly undermines the conclusion we are trying to strengthen. Any way you look at it, “B” is the correct answer.

Answer choice “C” gives a possible alternative explanation to the evidence in the original experiments. In other words, it suggests there may be another way of interpreting the same results without relying on the existence of a fifth universal force. As a result, “C” actually weakens the argument. Since we are trying to strengthen the argument, “C” cannot be the correct answer. Get rid of it!

Answer choice “D” also weakens the argument by suggesting a profound lack of precision with respect to the experiments noted in the argument. If the experiments were not precise, this implies that any interpretation based on the data may be incorrect. However, we are looking for statements that confirm the possibility of the fifth universal force -- not imply that the force is merely noisy experimental data. “D” simply undermines the existing experiments.

Answer choice “E” is completely irrelevant to the logical gap. Whether other “exciting ideas” were being developed at the same time sheds no additional light on the possible existence of a fifth universal force. “E” is just context. We can quickly eliminate it.

In the end, only one answer choice even gets us close to strengthening the argument. Two answer choices ("A" and "E") provide context behind the story but don't focus on the logical gap. Two answer choices actually weaken the argument ("C" and "D".) Only one is left over. And it is total weak sauce. With Strengthen questions, people look for an answer that so perfectly fixes the logic that Aristotle himself rises from the grave and gives you a round of applause. But that approach is a deliberate trap in many GMAT questions. Don't fall for it. Notice even in the question stem that it reads, "most strengthens". You just need the answer choice that does it best. And "B" is the only one that gets close.