Inventor John Friedman created a prototype of the first flexible straw by inserting a screw into a paper straw and,...

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

• Inventor John Friedman
  • created a prototype of the first flexible straw
    • by inserting a screw into a paper straw
    • and, using dental floss,
      • binding the straw tightly around the ______
• When the floss and screw were removed,
  • the resulting corrugations in the paper
    • allowed the straw to bend easily over the edge of a glass.

Understanding the Meaning

Let's read from the beginning:

• 'Inventor John Friedman created a prototype of the first flexible straw'
  • So we're learning about how the flexible straw was invented

• 'by inserting a screw into a paper straw'
  • He started by putting a screw inside a paper straw
  • Notice: "a screw" - just ONE screw

• 'and, using dental floss, binding the straw tightly around the ______'

Now here's where we need to fill in the blank. He's binding (wrapping) the straw tightly around something.

Let's look at our choices:

• A: screw's thread's
• B: screws' threads
• C: screw's threads
• D: screws threads'

What do we notice? They're all about the screw and its threads, but they differ in where the apostrophes go - which affects whether we're talking about one or multiple screws, and whether the threads possess something.

Based on what we've read:

• We know there's only ONE screw - the text said "a screw" and later says "the screw"
  • So we need the singular possessive form: screw's (one screw possessing something)

• What does that screw possess? Its threads.
  • Threads are the spiral grooves that wind around a screw
  • A screw has multiple threads (not just one), so threads should be plural

• The threads themselves don't possess anything - they're just what's being wrapped around
  • So "threads" should NOT have an apostrophe

So we need: screw's threads (the threads belonging to the one screw)

That's Choice C!

Now let's read the rest to see the complete picture:

• 'When the floss and screw were removed, the resulting corrugations in the paper allowed the straw to bend easily'
  • After wrapping the floss tightly around the screw's grooves, they removed both items
  • This left grooves (corrugations) in the paper
  • These grooves let the straw bend

The complete meaning: Friedman wrapped a paper straw around the spiral threads of a screw using dental floss, and when he removed the screw and floss, the paper had grooves that allowed it to bend - creating the flexible straw!

GRAMMAR CONCEPT APPLIED

Using Possessive Forms with Singular Nouns

When something belongs to a single thing, we use the singular possessive form: add an apostrophe + s to the owner. The thing that's owned can be either singular or plural (and doesn't get an apostrophe unless it also owns something).

Pattern: [Single Owner]'s + [Thing(s) Owned]

Examples:

• The tree's branches
  • One tree possesses multiple branches
  • tree's = singular possessive
  • branches = plural (no apostrophe because the branches don't own anything)

• The car's wheels
  • One car possesses multiple wheels
  • car's = singular possessive
  • wheels = plural (no apostrophe)

• The building's windows
  • One building possesses multiple windows
  • building's = singular possessive
  • windows = plural (no apostrophe)

In this question:

• The screw's threads
  • One screw (mentioned as "a screw") possesses multiple threads
  • screw's = singular possessive
  • threads = plural, no apostrophe (the threads don't own anything)

Common mistake to avoid: Don't add an apostrophe to the second noun just because the first noun has one. Only use possessive form when something actually possesses/owns something else.