_______ left the detective agency after he discovered his partner was destroying evidence.
Which choice completes the text so that it conforms to the conventions of Standard English?
Sherlock, once a trusted investigator,
Sherlock, once a trusted investigator
Sherlock once a trusted investigator
Sherlock—once a trusted investigator,
Correct Answer: A
Choice A is the best answer. The phrase "once a trusted investigator" is a nonrestrictive appositive describing Sherlock. It requires a comma after the name and a comma after the phrase (before the verb "joined" or "left").
Choice B is incorrect because it is missing the closing comma. Choice C is incorrect because it lacks the opening comma. Choice D is incorrect because it pairs a dash with a comma, which is inconsistent.