Astronomers have documented systematic orbital deviations among distant Kuiper Belt objects that cannot be explained by the gravitational effects 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

• Astronomers have documented systematic orbital deviations
  • among distant Kuiper Belt objects
    • that cannot be explained by the gravitational effects of known planets,
• anomalies suggesting the presence of an undiscovered massive body
  • beyond Neptune [?] discovery of such a planet would fundamentally reshape our understanding of solar system architecture.

Understanding the Meaning

Let's start reading from the beginning:

The sentence tells us:

• "Astronomers have documented systematic orbital deviations among distant Kuiper Belt objects that cannot be explained by the gravitational effects of known planets"
  • Scientists have found unusual orbital patterns in distant Kuiper Belt objects
  • These patterns can't be explained by the planets we already know about

Then we get more description:

• "anomalies suggesting the presence of an undiscovered massive body beyond Neptune"
  • "Anomalies" is another way to describe those orbital deviations
  • These anomalies suggest there's an undiscovered massive body beyond Neptune

This is where we have the blank.

Let's look at the choices:

• We need to decide what punctuation (if any) goes after "Neptune"
• And whether we use "a discovery" or just "discovery"

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

After the blank, we have:

• "discovery of such a planet would fundamentally reshape our understanding of solar system architecture"
  • This is talking about what would happen if we found such a planet
  • It would fundamentally change how we understand the solar system

Now, what do we notice about the structure here?

Let's look at what we have before and after the blank:

BEFORE the blank:

• "Astronomers have documented systematic orbital deviations... beyond Neptune"
  • Subject: "Astronomers"
  • Verb: "have documented"
  • This is a complete thought that could stand alone as its own sentence

AFTER the blank:

• "A discovery of such a planet would fundamentally reshape our understanding..."
  • Subject: "discovery" (with the article "a" from most choices)
  • Verb: "would reshape"
  • This is also a complete thought that could stand alone

So we have TWO separate, complete thoughts here:

• Each has its own subject and verb
• Each could be its own sentence
• They express two related but distinct ideas

When we have two complete thoughts like this, they need to be properly separated. We can't just run them together with a comma or no punctuation - that would violate basic sentence structure rules.

The correct answer is C (Neptune. A) - we need a period to separate these two complete thoughts into two distinct sentences.

GRAMMAR CONCEPT APPLIED

Separating Complete Thoughts (Independent Clauses)

When you have two complete thoughts - each with its own subject and verb that could stand alone as a sentence - they must be properly separated. You have several options:

Option 1: Use a period (create two sentences)

• First complete thought: The experiment succeeded beyond expectations
• Second complete thought: The results will be published next month
• Properly separated: The experiment succeeded beyond expectations. The results will be published next month.

Option 2: Use a semicolon (keep as one sentence)

• Both parts must be complete and grammatically parallel
• The experiment succeeded beyond expectations; the results will be published next month.

Option 3: Use a comma + coordinating conjunction

• Coordinating conjunctions: and, but, or, nor, for, yet, so
• The experiment succeeded beyond expectations, and the results will be published next month.

What you CANNOT do:

• Use just a comma: "The experiment succeeded, the results will be published" (comma splice)
• Use no punctuation: "The experiment succeeded the results will be published" (run-on)

In this question:

• First complete thought: "Astronomers have documented systematic orbital deviations... beyond Neptune" (subject: Astronomers, verb: have documented)
• Second complete thought: "A discovery of such a planet would fundamentally reshape..." (subject: discovery, verb: would reshape)
• These are two separate, complete ideas that need full separation
• Answer: Period creating two sentences (Choice C: Neptune. A)