OG详解-OG5 文法 Q29

Choice D is the best answer. The sentence contrasts first-class levers and second-class levers, explaining that the fulcrum in a first-class lever is between the effort and the load, whereas in a second-class lever the load is between the effort and the fulcrum.
Choice A is incorrect. The sentence defines two terms associated with levers; it doesn’t contrast first-class levers and second-class levers. Choice B is incorrect. While the sentence seems to acknowledge a general difference in fulcrum and load locations between first-class and second-class levers, it does not specify what this difference is. Moreover, the sentence could be read as emphasizing a similarity—that in both types of levers, the fulcrum and load are in different locations. The sentence thus fails to effectively contrast the two types of levers.Choice C is incorrect. The sentence describes a similarity between first-class and second-class levers; it doesn’t contrast them.