About 70,000 meteorites have been found on Earth. Although most meteorites are fragments of ______ blank

Choice B is the best answer. This choice uses a comma to correctly separate the dependent clause "although…asteroids" from the independent clause "several hundred have been…Mars."

Choice A is incorrect. This choice results in a sentence fragment. "Although…asteroids" is a dependent clause. It can’t stand on its own as a sentence, which means it can’t end in a period. Choice C is incorrect. This choice results in a punctuation error. "Although…asteroids" is a dependent clause and can’t be joined to the independent clause "several hundred have been…Mars" with a semicolon. A semicolon can only join two independent clauses. Choice D is incorrect. This choice creates a punctuation error. A colon can only come after an independent clause, but "although…asteroids" is a dependent clause.