SAT Question f735493e: Transitions answer and explanation

Choice A is incorrect because "on the contrary" illogically signals that the information in this sentence directly opposes the heating technique in the previous sentence. Instead, the vessel turns black as a result of that technique.

Choice B is incorrect because "for example" illogically signals that the information in this sentence is an example of the heating technique in the previous sentence. Instead, the vessel turns black as a result of that technique.

Choice C is incorrect because "previously" illogically signals that the information in this sentence occurs earlier in a chronological series of events than does the heating technique discussed in the first two sentences. Instead, the vessel turns black as a result of that technique.