OFFICIAL EXPLANATION


The correct answers are B and C.

The key word of this sentence is "merely," which implies a deficiency of some sort. A thrill that is merely fleeting would be deficient, and choices B, "evanescent," and C, "ephemeral," both mean "fleeting." Choice A, "deleterious," means "harmful," but riding a roller coaster only creates the sensation of defying death; it is not necessarily dangerous or harmful in reality. Choice D ,"invariable," means "constant," which is the opposite meaning of the correct answers. Choice E, "breathtaking," means "exciting," so using it in this context would be like saying "the excitement they derive is merely exciting," which is redundant. Choice F, "incorrigible," means "unchangeable," which does not make sense in this context.