In the 1960s, wildlife biologists documented only a handful of gray wolves surviving in isolated pockets of the northern wilderness....

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 the 1960s,
  • wildlife biologists documented only a handful of gray wolves
    • surviving in isolated pockets of the northern wilderness.
• By the early 2000s,
  • what had been a critically endangered species
    • teetering on the brink of extinction
  • had rebounded into something far more promising [?] a stable population of over 400 wolves
    • that transformed the ecosystem
      • by controlling elk populations and
      • allowing vegetation to recover.

Where [?] represents:

• A: ; a
• B: , it was a
• C: : a
• D: . A

Understanding the Meaning

The first sentence sets up the contrast:

• 'In the 1960s, wildlife biologists documented only a handful of gray wolves surviving in isolated pockets of the northern wilderness.'
  • This tells us the starting point – wolves were nearly extinct, with just a few surviving in remote areas.

Now the second sentence shows us what changed:

• 'By the early 2000s, what had been a critically endangered species teetering on the brink of extinction had rebounded into something far more promising...'
  • The wolves went from nearly extinct to 'something far more promising'
  • But we don't yet know what that 'something' is – the sentence is building anticipation

This is where we have the blank.

Let's look at the choices:

• They differ in punctuation (semicolon, comma, colon, or period)
• Some add extra words ('it was')
• Some capitalize the next word

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

The sentence continues: '...a stable population of over 400 wolves that transformed the ecosystem by controlling elk populations and allowing vegetation to recover.'

Now let's understand what this is telling us:

• 'A stable population of over 400 wolves'
  • This is the specific answer to what that 'something far more promising' is
  • It's not just 'promising' anymore – it's an actual stable population with real numbers
• 'That transformed the ecosystem by controlling elk populations and allowing vegetation to recover'
  • This explains why this population was so significant
  • The wolves didn't just survive – they changed the whole ecosystem

What do we notice about the structure here?

• Before the blank: 'had rebounded into something far more promising'
  • This is a complete thought grammatically
  • BUT it creates anticipation – we want to know WHAT that 'something' is
• After the blank: 'a stable population of over 400 wolves...'
  • This starts with a noun phrase (not a complete sentence)
  • It's providing the specific information – defining what that 'something' is
• The relationship:
  • We have a complete statement that introduces something
  • Followed by a descriptive phrase that explains exactly what that something is

So we need: a colon (Choice C)

The colon signals 'here comes the specific information I just promised you.' The word 'a' stays lowercase because what follows the colon is a phrase explaining the previous statement, not a new independent sentence.

GRAMMAR CONCEPT APPLIED

Using Colons to Introduce Explanations

When you have a complete statement followed by information that explains, specifies, or elaborates on what you just mentioned, you use a colon. The colon signals to the reader: 'Here's the specific information about what I just said.'

Pattern:

• Complete statement (often introducing or referencing something)
• Colon (:)
• Explanation/specification (can be a phrase or a complete sentence)

Example 1:

• With colon: The study revealed something unexpected: a connection between sleep patterns and academic performance.
  • 'The study revealed something unexpected' = complete statement that creates anticipation
  • 'a connection between sleep patterns and academic performance' = the specific explanation of what was unexpected

Example 2:

• With colon: She had one goal for the summer: to complete her novel.
  • 'She had one goal for the summer' = complete statement
  • 'to complete her novel' = specifies what that goal is

In our question:

• 'had rebounded into something far more promising' = complete statement introducing 'something'
• Colon
• 'a stable population of over 400 wolves...' = specifies exactly what that 'something' is

Note about capitalization: After a colon, keep the first word lowercase if what follows is a phrase or fragment. Capitalize only if what follows is a complete sentence (this is called an independent clause in grammar terms).