Typically, underlines, scribbles, and notes left in the margins by a former owner lower a book’s ______ when the former owner
is a famous poet like Walt Whitman, such markings, known as marginalia, can be a gold mine to literary scholars.
value, but
value
value,
value but
Choice A is the best answer. The convention being tested is the coordination of independent clauses within a sentence. An
independent clause is a phrase containing a subject and a verb that can stand on its own as a sentence. This choice uses a
comma and the coordinating conjunction “but” to join the ﬁrst independent clause (“underlines…lower a book’s value”) and
the second independent clause (“such markings…can be a gold mine to scholars”) to create a compound sentence.
Choice B is incorrect because it results in a run-on sentence. The two independent clauses are fused without punctuation
and/or a conjunction. Choice C is incorrect because it results in a comma splice. A comma can’t be used in this way to mark
the boundary between two independent clauses. Choice D is incorrect because a comma is needed to mark the boundary
between two coordinated independent clauses.