Which choice completes the text so that it conforms to the conventions of Standard English?
A
where sound is made?
B
where is sound made.
C
where sound is made.
D
where is sound made?
Explanation
Correct answer: C.
Choice C is the best answer. The convention being tested is end-of-sentence punctuation. This choice correctly uses a period to punctuate a declarative sentence ("the reed of a wind instrument is the mouthpiece") that ends with a prepositional phrase ("where sound is made").
Why the other choices are wrong
Choice A
Choice A is incorrect. It’s unconventional to use a question mark to punctuate a declarative sentence.
Choice B
Choice B is incorrect. The structure requires that the sentence continue as a declarative clause, not end with an interrogative clause.
Choice D
Choice D is incorrect. The structure requires that the sentence continue as a declarative clause and end with a period, not end with an interrogative clause and a question mark.