Marine biologists have studied coral reef ecosystems extensively since the 1960s ______ many fundamental questions about their resilience to climate...

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 biologists have studied coral reef ecosystems extensively since the 1960s (?)
• many fundamental questions about their resilience to climate change remain unanswered.

Understanding the Meaning

Let's start reading from the beginning:

The sentence tells us:

• "Marine biologists have studied coral reef ecosystems extensively since the 1960s"
  • This gives us a complete picture: marine biologists have been studying coral reefs for a long time - since the 1960s.

This is where we have the blank.

Let's look at the choices:

• A: adds ", yet"
• B: adds nothing
• C: adds just a comma
• D: adds "because"

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

The sentence continues:

• "many fundamental questions about their resilience to climate change remain unanswered"
  • Even though marine biologists have studied these ecosystems for decades, many basic questions about how coral reefs handle climate change still don't have answers.

What do we notice about the structure here?

• Both parts are complete thoughts:
  • "Marine biologists have studied coral reef ecosystems extensively since the 1960s" - could stand alone as a sentence
  • "many fundamental questions about their resilience to climate change remain unanswered" - could also stand alone as a sentence

• These two complete thoughts have a contrasting relationship:
  • First part: lots of study over many years
  • Second part: but questions still remain
  • This is a "despite this, that" kind of contrast

When we have two complete thoughts that contrast, we need to connect them properly with a comma plus a connecting word that shows contrast.

So we need: 1960s, yet

"Yet" is a connecting word (like "but") that shows contrast, and when we use it to join two complete thoughts, we need a comma before it.

GRAMMAR CONCEPT APPLIED

Connecting Two Complete Thoughts with Contrasting Meaning

When you have two complete thoughts (called independent clauses in grammar terms) that could each stand alone as sentences, and they express contrasting ideas, you connect them with a comma plus a coordinating conjunction that shows contrast:

Pattern:

• Complete thought 1, yet complete thought 2
• Complete thought 1, but complete thought 2

Example 1:

• Two separate sentences: "The team practiced every day. They lost the championship."
• Connected with contrast: "The team practiced every day, yet they lost the championship."
• Shows the contrast between effort and outcome

Example 2:

• Two separate sentences: "Scientists have collected massive amounts of data. They cannot predict earthquakes reliably."
• Connected with contrast: "Scientists have collected massive amounts of data, yet they cannot predict earthquakes reliably."
• Shows the contrast between data collection and prediction ability

In this question:

• First complete thought: "Marine biologists have studied coral reef ecosystems extensively since the 1960s"
• Second complete thought: "many fundamental questions about their resilience to climate change remain unanswered"
• These contrast (despite study, questions remain), so we connect them with ", yet"

Important:

• Without the conjunction = run-on sentence
• With only comma = comma splice
• With comma + "yet" = correct connection