<span>The answer is: [B]:
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"Kotowski cites four scholars who specialize in the study of volcanoes, whereas Ferguson cites only the encyclopedia." .
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A complex sentence contains one independent clause and at least one dependent clause. Here, in your example, there are two simple independent clauses which you need to merge using a dependent adjectival clause in order to make one complex sentence. Here is how to do it:
The boy <u>who wore a green coat</u><u /> carried his sister home.
