Eli Eisenberg, a genetics expert at Tel Aviv University in Israel, recently discovered that ________ have a special genetic ability...

Let's begin by understanding the meaning of this sentence. We'll use our understanding of pause points and segment the sentence as shown - understanding and assimilating the meaning of each segment bit by bit!

Sentence Structure

• Eli Eisenberg,
  • a genetics expert at Tel Aviv University in Israel,
• recently discovered that
  • ______ [cephalopods / ocean dwellers that include the squid, the octopus, and the cuttlefish (?)]]
    • have a special genetic ability called RNA editing
      • that confers evolutionary advantages.

Understanding the Meaning

The sentence starts by introducing someone:

• Eli Eisenberg,
  • a genetics expert at Tel Aviv University in Israel

So we know who we're talking about – a genetics researcher.

Now the sentence tells us what this researcher did:

• recently discovered that...

This is where we have the blank. Let's look at the choices:

• All four choices start with "cephalopods"
• All four add the same descriptive information: "ocean dwellers that include the squid, the octopus, and the cuttlefish"
• What varies is HOW this descriptive information is punctuated

To see what works here, let's read the rest of the sentence and understand what it's saying!

After the blank, the sentence continues:

• have a special genetic ability called RNA editing
  • that confers evolutionary advantages

So the complete thought is:

• Eisenberg discovered that cephalopods have a special genetic ability

Now, what do we notice about the structure here?

• "cephalopods" is the subject
  • It's the thing that HAS the genetic ability
• "have a special genetic ability" is the verb and what follows
  • This is the main action – what the cephalopods do
• "ocean dwellers that include the squid, the octopus, and the cuttlefish" is descriptive information
  • It's explaining what cephalopods are
  • It's coming RIGHT BETWEEN the subject (cephalopods) and the verb (have)
  • This is extra information – we could remove it and still have: "cephalopods have a special genetic ability"

When we have extra descriptive information that interrupts between a subject and its verb, we need to set off that ENTIRE descriptive phrase with matching punctuation on BOTH sides – like putting bookends around it.

In this case:

• The complete descriptive phrase is: "ocean dwellers that include the squid, the octopus, and the cuttlefish"
• This whole phrase needs to be enclosed with matching punctuation

So we need: cephalopods—ocean dwellers that include the squid, the octopus, and the cuttlefish—have...

The correct answer is Choice D because it uses matching dashes to enclose the complete descriptive phrase.

GRAMMAR CONCEPT APPLIED

Setting Off Non-Essential Descriptive Phrases with Matching Punctuation

When you add descriptive information that's non-essential (meaning the sentence would still make sense without it), you must set it off with matching punctuation on BOTH sides. This type of descriptive phrase is called a non-restrictive modifier in grammar terms.

You can use three types of matching punctuation:

• Two commas: The scientist, an expert in marine biology, published her findings
• Two dashes: The scientist—an expert in marine biology—published her findings
• Two parentheses: The scientist (an expert in marine biology) published her findings

The key rules:

1. The punctuation must match (both commas, both dashes, or both parentheses)
2. It must enclose the COMPLETE descriptive phrase
3. It must not interrupt or separate parts of the descriptive phrase itself

In our question:

• Subject: cephalopods
• Complete descriptive phrase: ocean dwellers that include the squid, the octopus, and the cuttlefish
• Verb: have

The structure needs to be:

• cephalopods—[complete descriptive phrase]—have...

Why dashes here? Dashes are particularly useful when:

• The descriptive phrase itself contains commas (as this one does with the list of examples)
• You want to emphasize or draw attention to the descriptive information

Choice D correctly uses matching dashes around the entire descriptive phrase, keeping the subject and verb clearly connected while setting off the non-essential information.