Dr. Rocío Paola Caballero-Gill is a paleoceanographer. This means that Dr. Caballero-Gill doesn't just study oceans as they are today....

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:
  • Dr. Rocío Paola Caballero-Gill is a paleoceanographer.
• Sentence 2:
  • This means that
    • Dr. Caballero-Gill doesn't just study oceans as they are today.
• Sentence 3:
  • She uses chemistry and fossil evidence [? has studied/to study/studied/studies] oceans as they were in the past.

Understanding the Meaning

Let's start from the beginning:

Sentence 1 tells us:

• Dr. Rocío Paola Caballero-Gill is a paleoceanographer.
  • This establishes her profession.

Sentence 2 explains what that means:

• 'This means that Dr. Caballero-Gill doesn't just study oceans as they are today.'
  • So being a paleoceanographer involves more than studying current oceans.

Now we get to Sentence 3, which tells us what else she does:

• 'She uses chemistry and fossil evidence _____ oceans as they were in the past.'

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

• has studied, to study, studied, studies

To see what works here, let's understand what this sentence is telling us!

The sentence structure is:

• 'She uses chemistry and fossil evidence'
  • 'uses' is telling us the main action - what she does
  • 'chemistry and fossil evidence' are the tools she uses

Now what comes next needs to tell us:

• WHY she uses these tools, or
• WHAT PURPOSE these tools serve

When we continue reading: '_____ oceans as they were in the past'

• This is telling us the purpose - studying ancient oceans
• We need a form that expresses purpose or intention

What do we notice about the structure here?

• 'Uses' is the main action
• We need something that explains what purpose those tools serve
• The pattern is: uses [tools] _____ [what she does with those tools]

When we want to express purpose - to explain WHY someone does something - we use the infinitive form:

• She uses chemistry and fossil evidence TO STUDY oceans

So we need Choice B: to study

This creates the complete meaning:

• She uses chemistry and fossil evidence (the tools)
• to study oceans as they were in the past (the purpose of using those tools)

GRAMMAR CONCEPT APPLIED

Using Infinitives to Express Purpose

When you want to explain WHY someone does something or WHAT PURPOSE an action serves, you use the infinitive form (called 'infinitive of purpose' in grammar terms) - that's 'to' plus the base form of a verb:

Pattern: [Subject] + [main verb] + [object] + [to + verb] + [additional information]

Examples:

Example 1:

• She uses tools to fix cars.
• Main action: uses tools
• Purpose: to fix cars (why she uses the tools)

Example 2:

• Scientists collect data to understand climate patterns.
• Main action: collect data
• Purpose: to understand climate patterns

In our question:

• She uses chemistry and fossil evidence to study oceans as they were in the past.
• Main action: uses chemistry and fossil evidence
• Purpose: to study oceans (what she does with those tools)

The infinitive 'to study' depends on the main verb 'uses' and tells us the purpose or intention behind the action. It's not competing as another main verb - it's providing crucial information about why the main action happens.