During the 1920s renovation of Chicago's Auditorium Theatre, engineers marveled at the building's original infrastructure. The structure's ______ the ...

Sentence Structure

• Sentence 1:
  • During the 1920s renovation of Chicago's Auditorium Theatre,
  • engineers marveled at the building's original infrastructure.
• Sentence 2:
  • The structure's framework [?]
  • the massive iron trusses that transferred roof weight to exterior walls—
  • had allowed architects to create an interior space completely free of support columns.

Understanding the Meaning

Let's start with the first sentence:

• "During the 1920s renovation of Chicago's Auditorium Theatre, engineers marveled at the building's original infrastructure."

This gives us the context:

• Engineers were doing renovation work in the 1920s, and they were really impressed by how the building was originally constructed.

Now the second sentence starts:

• "The structure's framework..."

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

• Our options are: em dash, no punctuation, comma, or semicolon after "framework"

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

The sentence continues:

• "the massive iron trusses that transferred roof weight to exterior walls—had allowed architects to create an interior space completely free of support columns."

Now let's really understand what this is telling us:

• "The structure's framework"
  • This is the subject – what the sentence is about
  • We're talking about the building's structural framework
• "the massive iron trusses that transferred roof weight to exterior walls"
  • This is explaining WHAT the framework was – specifically, it was these iron trusses
  • These trusses did something clever: they moved the weight of the roof to the outside walls
• "had allowed architects to create an interior space completely free of support columns"
  • This is the main verb and action of the sentence: "had allowed"
  • The result: because of how this framework worked, architects could design the inside without needing columns holding up the ceiling

So the complete picture is:

• The framework (which was specifically these iron trusses) had allowed architects to create a column-free interior space.

What do we notice about the structure here?

• There's already an em dash AFTER "exterior walls" (before "had allowed")
  • This em dash is clearly marking something – it's closing off the explanatory phrase
• The phrase "the massive iron trusses that transferred roof weight to exterior walls" is sitting between the subject and the verb
  • Subject: "The structure's framework"
  • Interrupting explanation: what that framework actually was
  • Closing dash: —
  • Main verb: "had allowed"
• This interrupting material needs to be set off on BOTH sides
  • We have the closing dash already
  • We need an opening dash to pair with it

So we need an em dash after "framework" to open the interruption. The correct answer is Choice A: framework—

GRAMMAR CONCEPT APPLIED

Using Paired Em Dashes to Set Off Interrupting Information

When you want to insert explanatory or clarifying information that interrupts the main flow of a sentence, you can use a pair of em dashes (one to open the interruption and one to close it). This is especially useful when the interruption comes between major sentence elements like the subject and verb:

Pattern:

• Main structure begins — interrupting information — main structure continues

Examples:

Example 1: The framework—the massive iron trusses—had allowed architects to create open spaces.

• Subject: "The framework"
• Interrupting explanation: "the massive iron trusses" (tells us what the framework was)
• Main verb: "had allowed"
• The dashes mark where the interruption begins and ends

Example 2: The scientist—a specialist in marine biology—discovered three new species.

• Subject: "The scientist"
• Interrupting detail: "a specialist in marine biology"
• Main verb: "discovered"

In this question:

• The sentence structure is: The structure's framework — the massive iron trusses that transferred roof weight to exterior walls — had allowed...
• The phrase between the dashes is providing specific information about what the framework consisted of
• Because the closing dash is already in the sentence (after "walls"), we need the opening dash after "framework" to properly mark where the interruption begins

Why this matters: Paired em dashes (which work similarly to paired commas or paired parentheses in grammar terms) help readers understand that certain information is supplementary or explanatory, and they clearly mark where that extra information begins and ends so the main sentence structure remains clear.