To illustrate Albert Einstein's special theory of relativity, picture two jugglers: one juggling on a steadily moving parade float, the...

Sentence Structure

• To illustrate Albert Einstein's special theory of relativity,
  • picture two jugglers:
    • one juggling on a steadily moving parade float,
    • the other juggling while standing still on a sidewalk.
• The laws of physics are identical for both [?],
  • regardless of [?] motion relative to each other.
• But what,
  • Einstein wondered,
    • about the speed of light?

Understanding the Meaning

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!

The passage sets up a thought experiment:

• "To illustrate Albert Einstein's special theory of relativity, picture two jugglers"
  • We're being asked to imagine two jugglers
  • One is juggling on a moving parade float
  • The other is juggling while standing still on a sidewalk

Now the sentence tells us something important about physics:

• "The laws of physics are identical for both..."
  • This is where we reach our first blank

Let's look at our choices:

• They all have some form of "jugglers" but differ in apostrophe placement
• They also differ in the second blank: "they're" vs "there" vs "their"

To see what works, let's read the complete phrase and understand what it's saying:

• "The laws of physics are identical for both ______ regardless of ______ motion relative to each other."

Now let's break down what we need:

First blank - What form of "jugglers"?

• "The laws of physics are identical for both..."
  • We're talking about the two jugglers we just pictured
  • We need the simple plural form: "jugglers"
  • Not possessive - we're not saying something belongs to the jugglers
  • We're saying the laws are identical FOR them (they experience these laws)

Second blank - Which word?

• "regardless of ______ motion relative to each other"
  • Whose motion? The jugglers' motion
  • We need a possessive pronoun to show the motion belongs to them
  • "their motion" = the motion that belongs to them (correct)
  • "they're motion" = they are motion (doesn't make sense)
  • "there motion" = location word, not possessive (incorrect)

What do we notice about the structure here?

• The phrase "for both jugglers" uses a simple plural
  • We're identifying who experiences identical laws
  • No possession is happening
• The phrase "their motion" uses a possessive pronoun
  • We're showing whose motion we're talking about
  • The motion belongs to the jugglers

So we need: jugglers, regardless of their

The correct answer is Choice D.

The complete meaning: Einstein is saying that whether a juggler is moving (on the float) or standing still (on the sidewalk), the laws of physics work the same way for both of them, regardless of how they're moving relative to each other.

GRAMMAR CONCEPT APPLIED

Distinguishing Between Plural and Possessive Forms, and Choosing the Right Possessive Pronoun

This question tests two important concepts:

1. When to use simple plurals vs. possessives:

• Simple plural (no apostrophe): Use when you're just talking about more than one of something
  • Example: "The laws work for both jugglers" (just referring to two people)
• Possessive (with apostrophe): Use when something belongs to or is associated with the noun
  • Example: "The jugglers' skills are impressive" (the skills belong to the jugglers)

In our sentence, "for both jugglers" is simply identifying who experiences the laws - no possession involved.

2. Distinguishing between their/there/they're:

These homophones (words that sound alike) have completely different uses:

• their = possessive pronoun (shows ownership)
  • "their motion" = the motion that belongs to them
• they're = contraction of "they are"
  • "they're moving" = they are moving
• there = location or expletive
  • "over there" (location) or "there are many reasons" (expletive)

Test it: Try expanding "they're" to "they are" in the sentence. If it doesn't make sense, it's wrong!

• "regardless of they are motion" (incorrect)
• "regardless of their motion" (correct)