OG详解-OG7 文法 Q4

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’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.