Swedish scientists Eva Engvall and Peter Perlmann developed a method for measuring the concentration of different proteins in a biological...

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:
  • Swedish scientists Eva Engvall and Peter Perlmann
    • developed a method
      • for measuring the concentration of different proteins
        • in a biological sample.
• Sentence 2:
  • Their method [?] called ELISA (enzyme-linked immunosorbent assay),
    • is used to detect and measure proteins
      • that indicate the presence of certain diseases.
• Where [?] = the punctuation choice:
  • (called / —called / , called / called

Understanding the Meaning

Let's start from the beginning:

The first sentence tells us:

• Swedish scientists Eva Engvall and Peter Perlmann developed a method
  • for measuring protein concentration in biological samples.

Now the second sentence:

• "Their method..." - referring back to that method they developed.

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

• They differ in what punctuation (if any) comes before "called"
• We have: parenthesis, dash, comma, or nothing

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

• "called ELISA (enzyme-linked immunosorbent assay),"
  • This is telling us what the method is named - it's called ELISA
  • The parenthetical gives us what ELISA stands for
  • Notice there's a comma AFTER this whole phrase

• "is used to detect and measure proteins that indicate the presence of certain diseases."
  • This is telling us what the method does - its purpose

Now let's understand the structure here:

• "Their method" = the subject of the sentence
• "is used" = the main verb
• "called ELISA (enzyme-linked immunosorbent assay)" = extra descriptive information inserted between the subject and verb

So the core sentence is:

• "Their method is used to detect and measure proteins..."

And we're inserting this descriptive phrase:

• "called ELISA (enzyme-linked immunosorbent assay)"

What do we notice about the structure here?

• When you insert a descriptive phrase that gives extra information (but isn't essential to the main sentence), you need to set it off with matching punctuation on both sides.

• We can see there's already a comma AFTER the descriptive phrase
  • Right after "(enzyme-linked immunosorbent assay),"

• So we need matching punctuation BEFORE the phrase starts
  • That means we need a comma before "called"

The correct answer is Choice C: method, called

GRAMMAR CONCEPT APPLIED

Setting Off Non-Essential Descriptive Phrases with Matching Punctuation

When you insert a descriptive phrase into a sentence that provides extra information (but isn't essential to the core meaning), you need to set it off with matching punctuation on both sides. This is called a non-restrictive modifier in grammar terms.

The Matching Rule:

• Comma...comma
• Dash...dash
• Parenthesis...parenthesis

Example 1:

• Core sentence: The professor teaches biology
• With descriptive phrase: The professor, an expert in genetics, teaches biology
• Notice: comma before "an expert" and comma after "genetics"

Example 2:

• Core sentence: The city attracts millions of tourists
• With descriptive phrase: The city—known for its museums—attracts millions of tourists
• Notice: dash before "known" and dash after "museums"

In this question:

• Core sentence: Their method is used to detect and measure proteins...
• Descriptive phrase inserted: called ELISA (enzyme-linked immunosorbent assay)
• Structure: Their method, called ELISA (enzyme-linked immunosorbent assay), is used to...
• Comma before "called" matches the comma after the parenthetical

The key is recognizing that the descriptive information is being inserted into the main sentence flow, so it needs matching punctuation to show where it begins and ends.