Many coral species thrive in shallow, sunlit ______ others have adapted to survive in the darkness of deep ocean trenches.

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

• Many coral species
  • thrive
    • in shallow, sunlit waters [?]
• others
  • have adapted
    • to survive
      • in the darkness of deep ocean trenches.

Understanding the Meaning

Let's start reading from the beginning:

'Many coral species thrive in shallow, sunlit waters'

• This is telling us about coral species that do well in shallow waters where sunlight reaches.

This is where we have the blank.

Let's look at the choices:

• A gives us just a comma
• B gives us nothing
• C gives us "but" without a comma
• D gives us a comma followed by "but"

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

The sentence continues: 'others have adapted to survive in the darkness of deep ocean trenches.'

• This is telling us about different coral species (the "others")
• These have adapted to survive in deep, dark ocean trenches
• This is a very different environment from the shallow, sunlit waters!

So the complete picture is:

• Some coral species thrive in shallow, sunlit waters
• BUT other coral species have adapted to deep, dark trenches
• These are two contrasting facts being presented

What do we notice about the structure here?

Let me look at each part:

• 'Many coral species thrive in shallow, sunlit waters'
  • Subject: Many coral species
  • Verb: thrive
  • This is a complete thought that could stand alone as its own sentence

• 'others have adapted to survive in the darkness of deep ocean trenches'
  • Subject: others
  • Verb: have adapted
  • This is also a complete thought that could stand alone as its own sentence

So we have two complete thoughts that need to be joined together, and they have a contrasting relationship (shallow vs. deep, sunlit vs. dark).

When we join two complete thoughts that contrast with each other, we need:

• A connecting word like "but" to show the contrast
• A comma before that connecting word

The correct answer is D: waters, but

GRAMMAR CONCEPT APPLIED

Joining Two Complete Thoughts with Connecting Words

When you have two complete thoughts (each with its own subject and verb, able to stand alone as a sentence) and you want to join them with a connecting word (called coordinating conjunctions in grammar terms - words like "and," "but," "or," "so," "for," "nor," "yet"), you need to use this pattern:

Complete thought + comma + connecting word + complete thought

Examples:

Pattern 1 - Contrast with "but":

• Complete thought: The experiment succeeded
• Complete thought: The results were unexpected
• Joined correctly: The experiment succeeded, but the results were unexpected

Pattern 2 - Addition with "and":

• Complete thought: The temperature dropped rapidly
• Complete thought: Ice began forming on the lake
• Joined correctly: The temperature dropped rapidly, and ice began forming on the lake

In our question:

• Complete thought: Many coral species thrive in shallow, sunlit waters
• Complete thought: others have adapted to survive in the darkness of deep ocean trenches
• Relationship: Contrast (some corals like one environment BUT others like a different one)
• Joined correctly: Many coral species thrive in shallow, sunlit waters, but others have adapted to survive in the darkness of deep ocean trenches

The comma before "but" is essential because both parts are complete thoughts. Without it, the sentence violates Standard English conventions.