We are asked to find an assumption. The assumption is the unstated notion that must be true if the conclusion is to stand. The argument involves a question of cause and effect. Since enrollment in graduate and professional programs tends to be high when the economy is strong and low when it is weak, the reason must be, according to the author, a matter of perceptions of job availability. Sounds reasonable, but do all the terms match up with those in this conclusion?
We know from the question stem that they do not. What is missing? Well, the evidence pertains to the state of the economy. But the conclusion strays into the area of psychology--perceptions. Are these the same things? The author treats them as such by arguing from evidence regarding the state of the economy to a conclusion based on perceptions of the economy. The author takes the relationship between these for granted, but technically, in order for the argument to work, this must be established. Choice (B) reveals this basic assumption.
