Many mechanical calculators were powered by a notched cylinder mechanism called the Leibniz wheel. Leibniz wheel calculators were popular in

Question

Many mechanical calculators were powered by a notched cylinder mechanism called the Leibniz wheel. Leibniz wheel calculators were popular in the first half of the twentieth blank these ingenious devices were eventually replaced by electronic calculators.

Which choice completes the text so that it conforms to the conventions of Standard English?

Accepted Answer

Choice C is the best answer. The convention being tested is the coordination of main clauses within a sentence. This choice correctly uses a comma and a coordinating conjunction ("but") to join the first main clause ("Leibniz...century") and the second main clause ("these ingenious...calculators"). Choice A is incorrect because it results in a run-on sentence. The two main clauses are fused without punctuation and/or a conjunction. Choice B is incorrect because it results in a comma splice. Without a conjunction following it, a comma can&rsquo;t be used in this way to join two main clauses. Choice D is incorrect because joining the two main clauses in this way with the subordinating conjunction "that" results in an ungrammatical and illogical sentence.

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