Horsepower is a unit of measurement used to determine how much power a vehicle produces. The

Choice C is the best answer. The convention being tested is the use of punctuation within a sentence. This choice uses a semicolon in a conventional way to join the first main clause ("The measurement...moved") and the second main clause ("for example...second").

Choice A is incorrect because it results in a comma splice. Without a coordinating conjunction, a comma can’t be used in this way to join the two main clauses ("The measurement…moved" and "for example…second"). Choice B is incorrect because it results in a comma splice. Without a conjunction following it, a comma can’t be used in this way to join the two main clauses ("The measurement…moved" and "one unit…second"). Choice D is incorrect because it results in a run-on sentence. The two main clauses ("The measurement…moved" and "one unit…second") are fused without punctuation and/or a conjunction.