Eli Eisenberg, a genetics expert at Tel Aviv University in Israel, recently discovered that _______have a special genetic ability called RNA editing that confers evolutionary advantages.
Which choice completes the text so that it conforms to the conventions of Standard English?
Explanation
Context: The sentence introduces cephalopods and then sets off a nonessential appositive ("ocean dwellers that include the squid, the octopus, and the cuttlefish") using em dashes. The appositive is placed between the subject "cephalopods" and the predicate "have a special genetic ability."
Answer: D) cephalopods—ocean dwellers that include the squid, the octopus, and the cuttlefish—
Why? Paired em dashes correctly enclose the nonessential appositive. The opening em dash comes after "cephalopods," and the closing em dash comes after "cuttlefish," allowing the main clause to continue naturally.
Traps:
- A) cephalopods, ocean dwellers that include the squid, the octopus, and the cuttlefish → commas are insufficient when the appositive itself contains commas; em dashes create clearer separation
- B) cephalopods—ocean dwellers—that include the squid, the octopus, and the cuttlefish, → misplaces the second em dash mid-appositive, then adds a comma — unmatched structure
- C) cephalopods, ocean dwellers that include: the squid, the octopus, and the cuttlefish, → a colon mid-appositive and surrounding commas are structurally incorrect