Marine biologist Dr. Elena Vasquez has dedicated her career to understanding the resilience of coastal ecosystems in the face of...

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

• Marine biologist Dr. Elena Vasquez
  • has dedicated her career
    • to understanding the resilience of coastal ecosystems
      • in the face of climate change.
• Working to identify coral species
  • most resistant to warming waters[?]
• Vasquez
  • has established research stations
    • throughout the Caribbean
      • where she monitors reef recovery patterns.

Understanding the Meaning

The first sentence is straightforward:

• Marine biologist Dr. Elena Vasquez has dedicated her career to understanding how coastal ecosystems stay resilient when facing climate change.

Now the second sentence:

• 'Working to identify coral species most resistant to warming waters'
  • This describes what Vasquez is doing as part of her work
  • She's trying to find out which types of coral can best handle warmer water

This is where we have the blank.

Let's look at the choices:

• The choices give us different punctuation marks after 'waters'
  • A semicolon
  • A comma
  • No punctuation at all
  • A period

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

The sentence continues:

• 'Vasquez has established research stations throughout the Caribbean where she monitors reef recovery patterns'
  • This is telling us the main action - what Vasquez HAS DONE
  • She set up research stations in the Caribbean
  • At these stations, she watches how reefs recover

So the complete picture is:

• While working to identify resistant coral species, Vasquez has established research stations where she monitors reef recovery.

What do we notice about the structure here?

• 'Working to identify coral species most resistant to warming waters'
  • This is an introductory phrase that describes what Vasquez is doing
  • It gives us background context
  • But it's NOT a complete thought on its own - it needs the main part of the sentence
• 'Vasquez has established research stations...'
  • This IS the complete thought - it has a subject (Vasquez) and a main verb (has established)
  • This is what the sentence is fundamentally about

When you have an introductory descriptive phrase (especially one that starts with an -ing verb like 'Working'), you need to separate it from the main part of the sentence with a comma.

So we need Choice B: a comma after waters.

GRAMMAR CONCEPT APPLIED

Using Commas with Introductory Phrases

When you begin a sentence with an introductory phrase (called a participial phrase in grammar terms when it starts with an -ing verb form), you must use a comma to separate it from the main clause:

Pattern:

• [Introductory phrase describing action], [Subject + Main Verb + rest of sentence]

Example 1:

• Introductory phrase: Running down the street
• Main clause: John spotted his friend
• Complete sentence: Running down the street, John spotted his friend.

Example 2:

• Introductory phrase: Hoping to improve test scores
• Main clause: the school implemented a new tutoring program
• Complete sentence: Hoping to improve test scores, the school implemented a new tutoring program.

In this question:

• Introductory phrase: Working to identify coral species most resistant to warming waters
• Main clause: Vasquez has established research stations throughout the Caribbean where she monitors reef recovery patterns
• Complete sentence: Working to identify coral species most resistant to warming waters, Vasquez has established research stations throughout the Caribbean where she monitors reef recovery patterns.

The comma signals to the reader: "The introductory description is done; now here comes the main point of the sentence."