Chondrites are stony meteorites that are undifferentiated - that is, their contents have not melted and separated into distinct layers....

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

SENTENCE 1:

• Chondrites
  • are stony meteorites
    • that are undifferentiated—
      • that is,
      • their contents have not melted and separated
        • into distinct layers.

SENTENCE 2:

• They
  • are hardly pristine [?] many chondrites
    • experience aqueous alteration
      • as a result of exposure to fluids,
    • as well as fracturing, veining, and localized melting
      • due to collisions with other objects.

• Where [?] = what varies in the choices (punctuation around "though")

Understanding the Meaning

The first sentence tells us about chondrites:

• They're stony meteorites that are undifferentiated
  • meaning their contents haven't melted and separated into distinct layers

The second sentence continues:

• "They are hardly pristine..."

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

• All choices include the word "though"
• They vary in how "though" is punctuated:
  • A: pristine, though
  • B: pristine, though;
  • C: pristine; though
  • D: pristine, though,

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

The sentence continues:

• "many chondrites experience aqueous alteration as a result of exposure to fluids, as well as fracturing, veining, and localized melting due to collisions with other objects"

So the complete meaning is:

• Chondrites are hardly pristine (not unchanged/perfect)
  • because many of them experience various forms of alteration—
    • exposure to fluids causing aqueous alteration
    • fracturing
    • veining
    • localized melting from collisions

What do we notice about the structure here?

Let's look at what comes before and after "though":

• BEFORE "though": "They are hardly pristine"
  • Subject: They
  • Verb: are
  • This is a complete thought that could stand alone

• AFTER "though": "many chondrites experience aqueous alteration..."
  • Subject: many chondrites
  • Verb: experience
  • This is also a complete thought that could stand alone

So we have two complete thoughts (two independent clauses) that need to be connected. "Though" is acting as a transitional word linking these two ideas.

When you connect two complete thoughts with a transitional word like "though," you need specific punctuation:

• A comma before the transitional word (to set it off from the first clause)
• A semicolon after the transitional word (to properly separate the two independent clauses)

So we need: pristine, though; many chondrites experience...

The correct answer is Choice B: pristine, though;

GRAMMAR CONCEPT APPLIED

Connecting Two Complete Thoughts with a Transitional Word

When you have two complete thoughts (called independent clauses in grammar terms) that you want to connect using a transitional word—like "though," "however," "therefore," or "nevertheless"—you need specific punctuation:

Pattern: First complete thought, transitional word; second complete thought.

Examples:

1. Two separate sentences:
   • The experiment failed. The researchers learned valuable information.
2. Connected with "however" as a transitional word:
   • The experiment failed, however; the researchers learned valuable information.
   • Comma before "however" (sets off the transitional word)
   • Semicolon after "however" (separates the two complete thoughts)
3. Another example with "therefore":
   • The data was inconclusive, therefore; we need to run additional tests.

In our question:

• First complete thought: "They are hardly pristine"
• Transitional word: "though"
• Second complete thought: "many chondrites experience aqueous alteration..."
• Correct punctuation: "They are hardly pristine, though; many chondrites experience..."

This punctuation properly sets off the transitional word and prevents a run-on sentence by correctly separating the two independent clauses.