The forty-seven geothermal springs of Arkansas' Hot Springs National Park are sourced via a process known as natural groundwater recharge,...

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

• The forty-seven geothermal springs of Arkansas' Hot Springs National Park
  • are sourced via a process known as natural groundwater recharge,
    • in which rainwater percolates downward through the earth—
      • in this case, the porous rocks of the hills around Hot Springs (?) to
  • collect in a subterranean basin.

Where (?) = nothing, colon, dash, or comma

Understanding the Meaning

Let's start reading from the beginning:

The sentence tells us that:

• The forty-seven geothermal springs of Arkansas' Hot Springs National Park
  • are sourced via a process known as natural groundwater recharge

So we're learning about how these springs get their water—through a process called "natural groundwater recharge."

The sentence then explains what this process involves:

• "in which rainwater percolates downward through the earth"
  • So rainwater seeps down through the earth

Then we see a dash: "—in this case, the porous rocks of the hills around Hot Springs"

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

• They differ in what punctuation comes after "Hot Springs"
• The choices are: nothing, a colon, a dash, or a comma

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

The sentence continues: "to collect in a subterranean basin"

• So after the rainwater percolates down, it collects in an underground basin

Now let's understand what the structure is telling us:

• The main flow describes what happens:
  • "rainwater percolates downward through the earth...to collect in a subterranean basin"

• But there's extra information inserted in the middle:
  • "in this case, the porous rocks of the hills around Hot Springs"
  • This clarifies what "the earth" specifically means in this situation

• Notice that this extra information was introduced with a dash after "earth"

What do we notice about the structure here?

• We have an interruption in the middle of the sentence
  • It started with a dash after "earth"
  • It provides clarifying information
  • Then the sentence needs to return to its main flow

• When you interrupt a sentence with a dash, you need another dash to close that interruption
  • Think of it like parentheses—you need both an opening and a closing mark
  • The structure should be: [main sentence]—[interruption]—[continuation]

So we need a dash after "Hot Springs" to close the interruption and signal the return to the main sentence flow.

The correct answer is C: "Hot Springs—to"

GRAMMAR CONCEPT APPLIED

Using Paired Dashes for Interruptions

When you want to insert extra information in the middle of a sentence, you can use paired dashes (called parenthetical dashes in grammar terms) to mark where the interruption begins and ends. The key rule: if you open with a dash, you must close with a dash.

The pattern looks like this:

Example 1:

• Without interruption: The committee reviewed the proposal and approved it.
• With interruption: The committee—all five members were present—reviewed the proposal and approved it.
• Main sentence: "The committee reviewed the proposal and approved it"
• Interruption: "all five members were present"
• Dashes mark both the beginning and end

Example 2:

• Without interruption: The study examined students from diverse backgrounds to understand learning patterns.
• With interruption: The study examined students from diverse backgrounds—including urban, suburban, and rural schools—to understand learning patterns.
• Main sentence: "The study examined students from diverse backgrounds to understand learning patterns"
• Interruption: "including urban, suburban, and rural schools"
• Dashes create symmetrical boundaries

In this question:

• Main sentence flow: "rainwater percolates downward through the earth...to collect in a subterranean basin"
• Interruption: "in this case, the porous rocks of the hills around Hot Springs"
• First dash after "earth" opens the interruption
• Second dash after "Hot Springs" closes it and returns to the main flow

The symmetry is essential—both marks must match!