Source: GMAT Prep

Half of the subjects in an experiment- the experimental group- consumed large quantities of a popular artificial sweetener. Afterward, this group showed lower cognitive abilities than did the other half of the subjects- the control group- who did not consume the sweetener. The detrimental effects were attributed to an amino acid that is one of the sweetener’s principal constituents.

Which of the following, if true, would best support the conclusion that some ingredient of the sweetener was responsible for the experimental results?

A, Most consumers of the sweetener do not consume as much of it as the experimental group members did.

B, The amino acid referred to in the conclusion is a component of all proteins, some of which must be consumed for adequate nutrition.

C, The quantity of the sweetener consumed by individuals in the experimental group is considered safe by federal food regulators.

D, The two groups of subjects were evenly matched with regard to cognitive abilities prior to the experiment.

E, A second experiment in which subjects consumed large quantities of the sweetener lacked a control group of subjects who were not given the sweetener.


please help me explain the OA

Thank you very much

IMO: D is clear winner here

conclusion:-- something in sweetener cause the less cognitive ability of one group.

Options:-

A) Agenda - consumer eating sweetener --> out of scope
B) Agenda - Nutrition, limit of protein --> out of scope
C) Agenda - Federal rules --> out of scope
D) Relevant --> they have same level before experiment, so sweetener must have caused something.
E) Agenda - second experiment --> irrelevant.

What is OA?

definitely (d).

if you EVER see a CR problem about an experiment designed to test some hypothesis, you should FIRST consider experimental control. i.e., the groups being studied should be absolutely identical in EVERY relevant way, except the variable whose effect is being tested.

in this case, since we're testing the effect of the sweetener, the groups should be relevant in every way except amount of sweetener consumed.
* prior cognitive ability is obviously relevant.
* other relevant aspects should also be equalized. for instance, the two groups should take the same battery of cognitive tests.
* variables that are irrelevant to the experiment (such as the hair color of the subjects) don't have to be equalized.