While exploring Nevada's Gypsum Cave in 1930, Seneca and Abenaki archaeologist Bertha Parker made her most famous discovery: the skull...

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

• While exploring Nevada's Gypsum Cave in 1930,
  • Seneca and Abenaki archaeologist Bertha Parker
    • made her most famous discovery:
      • the skull of a now-extinct ground sloth (Nothrotheriops shastensis)
        • alongside human-made tools.
• Parker's crucial finding
  • was the first [?] humans in North America
    • as far back as 10,000 years ago.

Understanding the Meaning

Let's start from the beginning and understand what's happening:

The first sentence gives us the context:

• While exploring Nevada's Gypsum Cave in 1930,
  • An archaeologist named Bertha Parker (who was Seneca and Abenaki)
  • was exploring a cave in Nevada
• She made her most famous discovery:
  • the skull of a now-extinct ground sloth
  • alongside human-made tools
  • This combination is important - animal remains AND human tools together

Now the second sentence tells us why this discovery mattered:

• 'Parker's crucial finding was the first...'

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

• places (present tense verb)
• placed (past tense verb)
• place (base form)
• to place (infinitive)

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

• '...humans in North America as far back as 10,000 years ago.'

So the complete thought is:

• Parker's finding was the first [something] to do with establishing that humans were in North America 10,000 years ago
  • The sloth skull plus human tools proved that people were there that long ago
  • This was apparently the FIRST evidence to establish this

What do we notice about the structure here?

• We have the pattern 'the first _______ humans'
  • This is telling us what Parker's finding was the first to do
  • The action is about establishing or positioning humans at that time period
• When we use ordinal numbers like 'first,' 'second,' 'third,' we follow a specific pattern:
  • 'the first to [verb]'
  • 'She was the first to arrive'
  • 'He was the first to climb that mountain'
  • 'This finding was the first to place humans...'

So we need to place - the infinitive form. The correct answer is D.

The meaning: Parker's crucial finding was the first evidence to establish/position humans in North America as far back as 10,000 years ago.

GRAMMAR CONCEPT APPLIED

Using Infinitives After Ordinal Numbers

When you use ordinal numbers (first, second, third, last, etc.) to describe who or what performed an action or achieved something, you follow them with the infinitive form (to + base verb):

Pattern: [ordinal number] + to + [verb]

Example 1:

• 'Neil Armstrong was the first person to walk on the moon.'
  • 'first' = ordinal number
  • 'to walk' = infinitive showing what action he was first to do

Example 2:

• 'She was the second student to finish the exam.'
  • 'second' = ordinal number
  • 'to finish' = infinitive showing what action she was second to do

Example 3:

• 'This discovery was the last piece of evidence to emerge from the site.'
  • 'last' = ordinal number
  • 'to emerge' = infinitive showing what action it was last to do

In our question:

• 'Parker's crucial finding was the first to place humans in North America as far back as 10,000 years ago.'
  • 'first' = ordinal number
  • 'to place' = infinitive showing what action it was first to do (establish the presence of humans at that time)

This construction (called an infinitive phrase in grammar terms) indicates that the subject achieved or performed the action described. The infinitive form is required - not a conjugated verb form.