According to a recent Stanford study, how well unsaturated vegetable oils such as olive oil, sunflower oil, and canola oil hold up health-wise when matched against saturated fats such as butter, margarine, and lard depend on what foods are eaten when fewer saturated fats are consumed . (A) depend on what foods are eaten when fewer saturated fats are consumed (B) depend on the foods that are eaten when less saturated fats are consumed (C) depend on the food that is eaten when less saturated fat is consumed (D) depends on the food that is eaten when less saturated fats are consumed (E) depends on what foods are eaten when fewer saturated fats are consumed https://www.nytimes.com/2018/01/29/well/good-fats-bad-fats.html But the best-established facts on dietary fats say otherwise. How well polyunsaturated vegetable oils hold up health-wise when matched against saturated fats like butter, beef fat, lard and even coconut oil depends on the quality, size and length of the studies and what foods are eaten when fewer saturated fats are consumed.

arbazfatmi1994 The basic rule is that we use singular unless there is a specific indication that we have a plural subject. Singular is the default. So "How well X happens" is going to be singular. The only related structure I can think of that lends itself to a plural verb is one in which the object "fills in" the subject: "What I need are people who can help me." But this kind of usage often ends up feeling off, and the GMAT might give us an option that rewrites entirely.