OG详解-OG9 文法 Q28

Choice D is the best answer. The sentence uses “whereas” to contrast the emissivities of the two fibers, noting that the emissivity of the reflective metal fibers was just 0.02, far lower than that of the silicon carbide fibers (0.74). 
Choice A is incorrect. The sentence emphasizes the ability of reflective metal fibers and silicon carbide fibers to emit heat; it doesn’t contrast the emissivities of the two fibers. Choice B is incorrect. The sentence states a law of thermodynamics: the amount of heat a material absorbs is equal to the amount it emits. The sentence doesn’t contrast the emissivity of reflective metal fibers with that of silicon carbide fibers. Choice C is incorrect. While the sentence includes a generalization about the emissivities of reflective metal fibers and silicon carbide fibers, it emphasizes Abebe’s plans for their use in a garment; it doesn’t contrast the emissivities of the two fibers.