The research team documented three distinct coral reef systems in the Caribbean—the Mesoamerican Barrier Reef (stretching from Mexico to Honduras),...

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 research team documented three distinct coral reef systems in the Caribbean—
  • the Mesoamerican Barrier Reef
    • (stretching from Mexico to Honduras),
  • the Florida Reef Tract,
  • and the Jardines de la Reina
    • (located off the coast of Cuba[?])
• revealing unprecedented biodiversity in each ecosystem.

Understanding the Meaning

The sentence starts by telling us what a research team did:

• 'The research team documented three distinct coral reef systems in the Caribbean—'
  • They identified and recorded information about three different reef systems
  • The dash after 'Caribbean' signals: 'here come the details about these three systems'

Now we get the list of the three systems:

• 'the Mesoamerican Barrier Reef (stretching from Mexico to Honduras),'
  • First system, with a note in parentheses about its location
  • Parenthesis closes, then comma
• 'the Florida Reef Tract,'
  • Second system, followed by comma
• 'and the Jardines de la Reina (located off the coast of Cuba'
  • Third and final system (note the 'and')
  • Another parenthetical note giving location information

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

• A gives us: Cuba)
• B gives us: Cuba)—
• C gives us: Cuba,
• D gives us: Cuba),

So we're deciding whether to just close the parenthesis, or add additional punctuation after closing it. To see what works here, let's read the rest of the sentence and understand what it's saying!

The sentence continues:

• 'revealing unprecedented biodiversity in each ecosystem'
  • This tells us the result or significance of the documentation
  • The team's work revealed biodiversity that hadn't been seen before

Now, what do we notice about the structure here?

The sentence opens with a dash after 'Caribbean' that introduces the detailed list of three systems. This dash is opening an interruption in the middle of the sentence.

Think of it this way:

• Main sentence flow: 'The research team documented three distinct coral reef systems in the Caribbean... revealing unprecedented biodiversity'
• But in the middle, we insert the detailed list of which three systems

When you use a dash to open an interrupting section like this in the middle of a sentence, you need a closing dash to return to the main flow of the sentence.

The structure is:

• Beginning of sentence — interrupting details — continuation of sentence

So we need:

• ) to close the parenthetical about Cuba's coast
• — to close the dash-opened list and return to the main sentence

The correct answer is Choice B: Cuba)—

This creates: (located off the coast of Cuba)— which properly closes both the parenthetical and the dash-introduced list, allowing 'revealing' to continue the main sentence.

GRAMMAR CONCEPT APPLIED

Using Paired Dashes to Set Off Interrupting Information

When you use a dash to introduce interrupting, elaborating, or explanatory information in the middle of a sentence structure, you need a second dash to close that interruption and return to the main sentence flow. These are called paired dashes (or em dashes in technical grammar terms).

The Pattern:

• Without interruption: The company announced record profits revealing strong market performance
• With paired dashes: The company announced record profits—including gains in three divisions—revealing strong market performance
• First dash opens the interruption
• Second dash closes it
• The sentence flow continues naturally

Another example:

• Main sentence: The study examined five factors affecting climate
• With interruption: The study examined five factors—temperature, precipitation, wind patterns, ocean currents, and solar radiation—affecting climate
• Dash opens the detailed list
• Second dash closes the list
• Main sentence continues

In our question:

• The sentence uses a dash after 'Caribbean' to introduce the detailed list of three reef systems
• After the list completes (including the parenthetical about Cuba), we need a closing dash
• This returns us to the main sentence: 'revealing unprecedented biodiversity in each ecosystem'
• Because we're also inside a parenthesis, we need )— (close parenthesis, then close dash-opened section)

The key principle: Opening dashes need closing dashes when the sentence continues after the interruption.