The _______ a salamander species native to Mexico—has the remarkable ability to regenerate lost limbs throughout its entire life.

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

• The axolotl [?] a salamander species native to Mexico—
• has the remarkable ability
  • to regenerate lost limbs
    • throughout its entire life.
• [?] = what punctuation/spacing comes before 'a'

Understanding the Meaning

Let's start reading from the beginning:

'The axolotl'

• This is what the sentence is about - our subject.

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

• A: axolotl,
• B: axolotl—
• C: axolotl:
• D: axolotl

We're deciding what punctuation (if any) should come before the word 'a.'

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

The sentence continues:

• 'a salamander species native to Mexico—'
  • This is telling us what an axolotl is - it's a type of salamander from Mexico.
  • Notice there's a DASH after 'Mexico'

Then:

• 'has the remarkable ability to regenerate lost limbs throughout its entire life'
  • This is the main point - what the axolotl can do.

What do we notice about the structure here?

If we remove the middle part about 'a salamander species native to Mexico,' the sentence would read:

• 'The axolotl has the remarkable ability to regenerate lost limbs...'

So the phrase 'a salamander species native to Mexico' is extra descriptive information that interrupts the main sentence flow.

Here's the key thing:

• This interrupting information needs to be set off by a PAIR of matching punctuation marks - like bookends on either side.
• We can already see there's a DASH (—) AFTER 'Mexico'
• So we need a DASH BEFORE 'a salamander species' to create the matching pair.

The correct answer is B: axolotl—

This creates: 'The axolotl—a salamander species native to Mexico—has the remarkable ability...'

The two dashes work together as a pair to set off the descriptive information in the middle.

GRAMMAR CONCEPT APPLIED

Setting Off Interrupting Information with Paired Punctuation

When you insert extra descriptive or explanatory information in the middle of a sentence (called parenthetical information in grammar terms), you need to set it off with a matching pair of punctuation marks. You have three options:

Option 1: Two commas

• The senator, a former teacher, supported education funding.

Option 2: Two dashes

• The senator—a former teacher—supported education funding.

Option 3: Two parentheses

• The senator (a former teacher) supported education funding.

The critical rule: You must use the same punctuation mark to both open and close the interrupting information. You cannot mix them.

In this question:

• Main sentence: 'The axolotl has the remarkable ability to regenerate lost limbs throughout its entire life'
• Interrupting information: 'a salamander species native to Mexico'
• Closing punctuation already given: dash (—)
• Therefore, opening punctuation must be: dash (—)
• Result: 'The axolotl—a salamander species native to Mexico—has the remarkable ability...'

Why dashes? Dashes create a strong, emphatic break and draw attention to the interrupting information. They're especially useful for longer descriptive phrases or when you want to emphasize the extra information.