The research team's expedition to the Mariana Trench, which began in early 2019, yielded unprecedented data about deep-sea _____ they...

Sentence Structure

• The research team's expedition to the Mariana Trench,
• which began in early 2019,
• yielded unprecedented data about deep-sea ecosystems[?]
• they documented over forty previously unknown species
• and
• collected samples from depths exceeding 10,000 meters.
•
• Choices vary: semicolon (;) | and | comma (,) | nothing

Understanding the Meaning

Let's start reading from the beginning:

The research team's expedition to the Mariana Trench -

• We're learning about a specific expedition
• The parenthetical note tells us it began in early 2019

yielded unprecedented data about deep-sea ecosystems

So the main point of the first part is:

• This expedition produced never-before-seen information about ecosystems in the deep ocean

This is where we have the blank: 'ecosystems [?]'

Let's look at the choices:

• We're deciding between a semicolon, the word "and", a comma, or nothing at all
• This tells us we're figuring out how to connect what comes before with what comes after

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

they documented over forty previously unknown species
and
collected samples from depths exceeding 10,000 meters.

Now let's understand what this second part is telling us:

• "They" (the research team) did two things:
  • documented over forty species no one had seen before
  • collected samples from extremely deep parts of the ocean (over 10,000 meters down)
• This is giving us specific details about the data they collected

What do we notice about the structure here?

• The first part has its own complete thought:
  • Subject: "The research team's expedition"
  • Action: "yielded unprecedented data"
  • This could stand alone as a sentence
• The second part also has its own complete thought:
  • Subject: "they"
  • Actions: "documented" and "collected"
  • This could also stand alone as a sentence
• So we have two complete sentences that are closely related in meaning
  • The second one is elaborating on the first - telling us specifically what that "unprecedented data" consisted of

When you have two complete thoughts that are this closely connected, you need a semicolon to join them properly.

The correct answer is A: semicolon (;)

GRAMMAR CONCEPT APPLIED

Connecting Two Complete Thoughts with a Semicolon

When you have two complete sentences (called independent clauses in grammar terms) that are closely related in meaning, you can join them with a semicolon instead of separating them with a period:

Pattern:

• Complete thought 1 ; complete thought 2
• Each part has its own subject and verb
• Each part could stand alone as a sentence
• The semicolon shows they're closely connected ideas

Example 1:

• Wrong: The expedition collected samples, they analyzed them in the lab. (comma splice)
• Correct: The expedition collected samples; they analyzed them in the lab.

Example 2:

• Wrong: The data was groundbreaking it changed scientific understanding. (run-on)
• Correct: The data was groundbreaking; it changed scientific understanding.

In this question:

• First complete thought: "The research team's expedition... yielded unprecedented data about deep-sea ecosystems"
• Second complete thought: "they documented over forty previously unknown species and collected samples from depths exceeding 10,000 meters"
• These are closely related (the second explains the first), so a semicolon perfectly connects them