OG详解-OG9 文法 Q25

Choice A is the best answer. “Specifically” logically signals that the information in this sentence—that the Sun releases charged particles that later collide with atoms, resulting in auroral light—provides specific, precise details about how auroras result from the Sun’s activity. 
Choice B is incorrect because “similarly” illogically signals that the information in this sentence is similar to the general information about auroras in the previous sentence. Instead, this sentence provides specific, precise details about how auroras form. Choice C is incorrect because “nevertheless” illogically signals that the information in this sentence is despite the general information about auroras in the previous sentence. Instead, this sentence provides specific, precise details about how auroras form. Choice D is incorrect because “hence” illogically signals that the information in this sentence is a result of the general information about auroras in the previous sentence. Instead, this sentence provides specific, precise details about how auroras form