When threatened by a predator, the octopus displays remarkable defensive behaviors. With the same precision that the species has evolved...

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

Sentence Structure

• When threatened by a predator,
• the octopus displays remarkable defensive behaviors.

• With the same precision
  • that the species has evolved over millions of years,
• it (?) its skin color to match its surroundings
• and disappears from view.

Understanding the Meaning

Let's start with the first sentence to understand the context:

• 'When threatened by a predator, the octopus displays remarkable defensive behaviors.'
  • This is setting the scene - telling us about what happens when an octopus is in danger.
  • The subject here is 'the octopus' (singular).

Now the second sentence, where we have the blank:

• 'With the same precision that the species has evolved over millions of years'
  • This is telling us HOW the octopus does what it's about to do - with precision that evolved over a long time.

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

• 'it _____ its skin color to match its surroundings'

Let's look at our choices. They're giving us different forms of a verb:

• A. change (plural or bare form)
• B. changes (singular present)
• C. are changing (plural continuous)
• D. were changing (plural past continuous)

What do we notice about the structure here?

• The subject of this sentence is 'it' - which refers back to 'the octopus' from the previous sentence.
• 'It' is singular.
• Even though there's a long descriptive phrase between the subject 'it' and the blank ('With the same precision that the species has evolved...'), the verb still needs to match 'it.'
• We're also talking about what the octopus does in general when threatened - this is a regular behavior, described in present tense (like 'displays' in the first sentence).

So we need a singular present tense verb: changes matches 'it.'

The complete picture is:

• The octopus, when threatened, changes its skin color with precision and disappears from view.

Grammar Concept Applied

Subject-Verb Agreement with Separated Elements

The verb in a sentence must agree with its subject in number - singular subjects take singular verbs, and plural subjects take plural verbs. This rule holds true even when the subject and verb are separated by descriptive phrases or other information.

The pattern:

• Singular subject: The octopus changes...
• With separation: The octopus, despite its small size, changes...
• Or: It changes... → It, with great precision, changes...

In this question:

• Subject: "it" (singular, referring to "the octopus")
• Separation: "With the same precision that the species has evolved over millions of years"
• Verb needed: "changes" (singular present)

The key is to identify the true subject ("it") and not be distracted by other nouns in the descriptive phrases (like "precision," "species," or "years"). The verb must agree with "it," regardless of what comes between them.