Neuroscientist Dr. Elena Martinez's investigation of synaptic plasticity in aging brains over two decades ______ four key mechanisms that preserve...

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

• Neuroscientist Dr. Elena Martinez's investigation
• of synaptic plasticity
  • in aging brains
• over two decades
• ______ (?)
• four key mechanisms
  • that preserve cognitive function,
  • including the formation of new neural pathways.

Understanding the Meaning

Let's read from the beginning:

'Neuroscientist Dr. Elena Martinez's investigation'

• This tells us what the sentence is about: an investigation
• It's Dr. Elena Martinez's investigation - she's a neuroscientist

'of synaptic plasticity in aging brains'

• This describes what the investigation studied
• Synaptic plasticity means how the connections in the brain can change
• Specifically, this is about aging brains

'over two decades'

• This tells us how long the investigation took - 20 years

Now here's where we need to fill in the blank:

• 'investigation... over two decades ______'

Let's look at our choices:

• A. have identified
• B. identifies
• C. identify
• D. are identifying

The word we need must work with 'investigation' as the subject.

• 'Investigation' is singular - we're talking about one investigation
• So we need a singular verb

Looking at our choices:

• A. have identified - plural (have goes with plural subjects)
• B. identifies - singular ✓
• C. identify - plural
• D. are identifying - plural (are goes with plural subjects)

We need B. identifies - it's the only singular verb that matches our singular subject 'investigation.'

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

'four key mechanisms that preserve cognitive function, including the formation of new neural pathways'

• The investigation identifies four key mechanisms
• These mechanisms help preserve cognitive function (keep the brain working well)
• One example: the formation of new neural pathways

So the complete meaning: Dr. Martinez conducted a 20-year investigation of how aging brains can change, and this investigation identifies four key ways that brains can preserve their ability to function well.

What do we notice about the structure here?

• The subject 'investigation' is separated from its verb by several phrases:
  • 'of synaptic plasticity in aging brains' - describes the investigation
  • 'over two decades' - tells when/how long
• These phrases contain plural nouns like 'brains' and 'decades'
• But those nouns aren't the subject - they're part of descriptive phrases
• The verb must agree with 'investigation' (singular), not with these other plural nouns

The correct answer is B. identifies.

GRAMMAR CONCEPT APPLIED

Matching Verbs to Subjects When They're Separated

When the subject and verb are separated by descriptive phrases, the verb must still agree with the actual subject - not with other nouns that appear in between. This is especially tricky when those in-between phrases contain plural nouns but your subject is singular (or vice versa).

The pattern to follow:

Identify the true subject:

• "The investigation of synaptic plasticity in aging brains over two decades identifies..."
• Subject: "investigation" (singular)
• In-between phrases: "of synaptic plasticity," "in aging brains," "over two decades"
• These phrases often start with words like "of," "in," "over," "for," "with" (called prepositions in grammar terms)
• Verb needed: singular ("identifies")

Don't be distracted by nearby plural nouns:

• "The study of ancient civilizations reveals surprising similarities"
• Subject: "study" (singular)
• Don't be fooled by "civilizations" (plural) - it's not the subject
• Verb: "reveals" (singular)

How this applies to our question:

• Subject: "investigation" (singular)
• Distracting plural nouns in between: "brains," "decades"
• Correct verb: "identifies" (singular)
• The sentence structure: investigation... identifies four key mechanisms

VERIFICATION OUTPUT

Content Genre: Sciences
Grammar Concept Tested: Subject-Verb Agreement
Sentence Complexity: Complex
Pattern: A