Human-made (synthetic) ﬁbers used in clothes and many other consumer products are more durable than most natural plant
______ the manufacture of synthetic ﬁbers requires toxic chemical solvents that can pollute air and water.
ﬁbers,
ﬁbers but
ﬁbers
ﬁbers, but
Choice D is the best answer. The convention being tested is the coordination of main clauses within a sentence. This choice
correctly uses a comma and the coordinating conjunction “but” to join the ﬁrst main clause (“Human-made...ﬁbers”) and the
second main clause (“the manufacture...water”).
Choice A 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 B is incorrect because when coordinating two longer main clauses such as these, it’s
conventional to use a comma before the coordinating conjunction. Choice C is incorrect because it results in a run-on
sentence. The two main clauses are fused without punctuation and/or a conjunction.