In marine biology, the giant Pacific octopus—along with numerous other cephalopod species inhabiting coastal waters—_____ remarkable problem-solving a...

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

• In marine biology,
• the giant Pacific octopus
  • —along with numerous other cephalopod species
    • inhabiting coastal waters—
• [demonstrates/demonstrate/are demonstrating/have demonstrated] (?)
• remarkable problem-solving abilities
  • that challenge traditional assumptions about invertebrate intelligence.

Understanding the Meaning

Let's start reading from the beginning:

'In marine biology'

• This sets the context – we're talking about the field of marine biology.

'the giant Pacific octopus'

• This is what the sentence is about – this is our main subject.

'—along with numerous other cephalopod species inhabiting coastal waters—'

• Notice the dashes on both sides?
  • This is extra information being tucked into the sentence.
  • It's telling us: hey, by the way, many other cephalopods in coastal waters do this too.
• The dashes signal this is interrupting, parenthetical information.

Now here's where we need to fill in the blank:

• 'the giant Pacific octopus _____ remarkable problem-solving abilities'

Let's look at our choices:

• A: demonstrates (singular)
• B: demonstrate (plural)
• C: are demonstrating (plural)
• D: have demonstrated (plural)

The key decision is: do we need a singular verb or a plural verb?

What do we notice about the structure here?

• Our true subject is 'the giant Pacific octopus' – that's singular.
• The phrase between the dashes 'along with numerous other cephalopod species' is interrupting information.
• Even though there are plural nouns mentioned in that interrupting phrase, they don't change what our verb needs to agree with.
• The verb must match the TRUE subject: 'the giant Pacific octopus' (singular).

So we need the singular verb: demonstrates

Now let's read the rest to see the complete picture:

'remarkable problem-solving abilities that challenge traditional assumptions about invertebrate intelligence'

• The octopus demonstrates these impressive problem-solving abilities,
• and these abilities challenge what scientists traditionally believed about how smart invertebrates (animals without backbones) can be.

The complete meaning: In marine biology, the giant Pacific octopus (and, by the way, many other coastal cephalopods too) demonstrates remarkable problem-solving abilities that challenge traditional ideas about invertebrate intelligence.

The correct answer is A: demonstrates

GRAMMAR CONCEPT APPLIED

Subject-Verb Agreement with Interrupting Phrases

When a subject is separated from its verb by an interrupting phrase (set off by dashes, commas, or parentheses), the verb must still agree with the TRUE subject, not with any nouns that appear in the interrupting phrase.

Pattern:

• Singular subject + [interrupting phrase with other nouns] + singular verb

Example 1:

• The CEO—along with several board members—approves the budget.
• Subject: "The CEO" (singular)
• Interrupting phrase: "along with several board members"
• Verb: "approves" (singular)

Example 2:

• The students, together with their teacher, are attending the conference.
• Subject: "The students" (plural)
• Interrupting phrase: "together with their teacher"
• Verb: "are" (plural)

In our question:

• Subject: "the giant Pacific octopus" (singular)
• Interrupting phrase (set off by dashes): "along with numerous other cephalopod species inhabiting coastal waters"
• Verb needed: "demonstrates" (singular)

Key insight: Phrases like "along with," "together with," "as well as," and "in addition to" introduce additional information but don't change whether the subject is singular or plural. The verb agrees with the main subject only.