On sunny days, dark rooftops absorb solar energy and convert it to unwanted heat, raising the surrounding air ________ a...

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

• On sunny days,
• dark rooftops
  • absorb solar energy
  • and convert it to unwanted heat,
    • raising the surrounding air temperature (?)
• a light-colored covering
  • to an existing dark roof,
    • either by attaching prefabricated reflective sheets
    • or spraying on a paint-like coating,
• helps combat this effect.

Understanding the Meaning

Let's start reading from the beginning:

• 'On sunny days, dark rooftops absorb solar energy and convert it to unwanted heat'
  • This explains the problem: dark roofs soak up the sun's energy and turn it into heat we don't want

• 'raising the surrounding air temperature'
  • This heat makes the air around the building hotter

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

• Some have "by adding" and some have just "adding"
• The punctuation varies: semicolon, comma, period, or nothing

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

The passage continues: 'a light-colored covering to an existing dark roof, either by attaching prefabricated reflective sheets or spraying on a paint-like coating, helps combat this effect.'

Let me break this down:

• 'a light-colored covering to an existing dark roof'
  • This is talking about putting a light-colored material on top of a dark roof

• 'either by attaching prefabricated reflective sheets or spraying on a paint-like coating'
  • These are the two methods: you can attach sheets or spray on a coating
  • This part just gives us more details about HOW to add the covering

• 'helps combat this effect'
  • The light covering helps fight against that heat problem mentioned earlier

Now, what do we notice about the structure here?

First, let's look at what we need before "a light-colored covering":

• If we use "by adding a light-colored covering...helps combat this effect"
  • "By adding" is a prepositional phrase - it can't be the subject of a sentence
  • We'd have "helps" as a verb with no subject - that doesn't work!

• If we use "Adding a light-colored covering...helps combat this effect"
  • "Adding a light-colored covering" acts as the subject (it's the thing doing the helping)
  • "helps" is the verb
  • This creates a complete sentence ✓

So we need just "adding" (not "by adding"). This eliminates choices A and D.

Now let's think about the punctuation:

• The first part: "On sunny days, dark rooftops absorb solar energy and convert it to unwanted heat, raising the surrounding air temperature"
  • This is a complete sentence - it has a subject (dark rooftops) and verbs (absorb and convert)

• The second part: "Adding a light-colored covering to an existing dark roof...helps combat this effect"
  • This is also a complete sentence - it has a subject (Adding a light-colored covering) and a verb (helps)

We have TWO complete sentences here. They each express a complete thought and could stand alone.

When we have two complete sentences, we need proper separation between them:

• Choice B uses just a comma
  • A comma alone can't join two complete sentences - that's called a comma splice
  • This doesn't follow the rules of Standard English

• Choice C uses a period
  • A period properly separates two complete sentences ✓
  • This is exactly what we need here

The correct answer is C: "temperature. Adding"

GRAMMAR CONCEPT APPLIED

Separating Complete Sentences

When you have two complete sentences (each with its own subject and verb, expressing a complete thought), they must be properly separated. You cannot just use a comma or run them together:

Two complete sentences that need separation:

1. "Dark rooftops raise air temperature"
2. "Adding light-colored covering helps combat this effect"

WRONG ways to connect them:

• With comma only: "Dark rooftops raise air temperature, adding light-colored covering helps" ✗ (comma splice)
• With no punctuation: "Dark rooftops raise air temperature adding light-colored covering helps" ✗ (run-on)

CORRECT ways to connect them:

• With period: "Dark rooftops raise air temperature. Adding light-colored covering helps" ✓
• With semicolon (if closely related): "Dark rooftops raise air temperature; adding light-colored covering helps combat this" ✓
• With comma + coordinating conjunction: "Dark rooftops raise air temperature, but adding light-colored covering helps combat this" ✓

In this specific question:

• The first sentence describes the problem (dark roofs create heat)
• The second sentence describes the solution (light-colored covering helps)
• These are two distinct complete thoughts that need proper separation
• A period provides that clear, proper separation

Additional note: The word "Adding" functions as a gerund (called this in grammar terms) - it's a verb form ending in "-ing" that acts as a noun and can serve as the subject of a sentence. In contrast, "by adding" is a prepositional phrase and cannot be a subject.