“On the whole,” Ms. Dennis remarked, “engineering students are lazier

OFFICIAL EXPLANATION

The conclusion that engineering students are lazier now than they used to be does not follow from the stated observation that fewer and fewer of Ms. Dennis’ students regularly do the work they are assigned. In fact, the conclusion is not in any way supported by the reported observation unless it is also true that failure to do the assigned work indicates laziness. That latter proposition must therefore be one of the tacit assumptions underlying the conclusion. B best expresses this assumption and is thus the correct answer.

A is incorrect. Ms. Dennis concludes that her students are lazy on the basis of what she sees as a consequence of that laziness. This choice suggests a cause of that laziness. But Ms. Dennis does not have to make any assumptions about the causes of that laziness in order to draw her conclusion. C is also incorrect. This comparison between the work demands on engineering students and those on other students is irrelevant to the question of whether the work habits of engineering students have changed over time. The fourth answer choice is incorrect. If Ms. Dennis believed that the reason for her own students’ decreasing performance was her own declining effectiveness, she would not think of her students as exemplifying trends among engineering students in general. The last answer choice is also incorrect. Whether laziness is outgrown is irrelevant to the question of whether work habits of engineering students have changed over time.