The flying buttress became a defining feature of Gothic cathedrals during the 12th century. This architectural _____ allowed builders to...

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:

• The flying buttress became a defining feature of Gothic cathedrals during the 12th century.

Sentence 2:

• This architectural innovation(?)which allowed builders to construct walls with large stained glass windows, revolutionized European ecclesiastical design for centuries.

Understanding the Meaning

Let's start reading from the beginning:

First sentence tells us:

• The flying buttress became a defining feature of Gothic cathedrals during the 12th century.
  • This establishes what we're talking about - a specific architectural element called the flying buttress.

Now the second sentence begins:

• 'This architectural innovation...'
  • "This" refers back to the flying buttress
  • We're now calling it an "innovation"

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

• They're showing us different punctuation options after "innovation"
  • To see what works here, let's read the rest of the sentence and understand what it's saying!

The sentence continues:

• '...which allowed builders to construct walls with large stained glass windows, revolutionized European ecclesiastical design for centuries.'

Now let's understand what this complete sentence is telling us:

• The main structure is:
  • "This architectural innovation... revolutionized European ecclesiastical design"
  • That's the core statement - the innovation revolutionized design

• But there's additional information inserted in the middle:
  • "which allowed builders to construct walls with large stained glass windows"
  • This phrase is giving us extra descriptive detail about the innovation
  • It's explaining HOW the innovation worked (it allowed for walls with large windows)

What do we notice about the structure here?

• We have a noun ("innovation") followed by extra descriptive information ("which allowed...")
  • This extra information is inserted before we get to the main verb ("revolutionized")
  • It's adding helpful details, but the sentence would still make sense without it: "This innovation revolutionized design"

• When we insert extra descriptive information like this - information that's helpful but not essential - we need to set it off with commas
  • One comma before it starts ("innovation, which...")
  • One comma after it ends ("...windows, revolutionized")

So we need: innovation, which

The comma signals that we're adding extra information before continuing to the main point of the sentence.

GRAMMAR CONCEPT APPLIED

Using Commas with Descriptive "Which" Clauses

When you add extra descriptive information about something using a "which" clause, you need to set it off with commas (this is called a non-restrictive or non-essential clause in grammar terms). This signals that you're providing additional details that are helpful but not necessary to identify what you're talking about:

Pattern:

• Noun + comma + "which" clause + comma + rest of sentence

Example 1:

• Without extra information: "The telescope revealed new galaxies."
• With extra information: "The telescope, which was built in 2015, revealed new galaxies."
• "The telescope" = the noun we're describing
• "which was built in 2015" = extra descriptive information
• Commas on both sides set off this additional detail

Example 2:

• Without extra information: "The new policy affected thousands of workers."
• With extra information: "The new policy, which took effect in January, affected thousands of workers."
• The "which" clause adds context but isn't essential to the main statement

In our question:

• Main structure: "This architectural innovation... revolutionized European ecclesiastical design"
• Extra information inserted: "which allowed builders to construct walls with large stained glass windows"
• Result: "This architectural innovation, which allowed builders to construct walls with large stained glass windows, revolutionized European ecclesiastical design for centuries."

The key is recognizing when information is extra detail versus essential identification. If you're already clear about what you're referring to (like "this architectural innovation"), the "which" clause needs commas.