The relationship between sleep patterns and cognitive performance has been extensively studied in neuroscience. Research on adolescents shows that irr...

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:

• The relationship between sleep patterns and cognitive performance
  • has been extensively studied
    • in neuroscience.

Sentence 2:

• Research on adolescents
  • shows
    • that irregular sleep schedules impair memory consolidation,
• while investigation of adult subjects
  • (?) [demonstrates/demonstrated/will demonstrate/had demonstrated]
    • that even moderate sleep restriction significantly reduces executive function.

Understanding the Meaning

Let's start with the first sentence:

• It tells us the topic: the relationship between sleep and how well our brains work (cognitive performance) has been studied a lot in neuroscience.

Now the second sentence gives us specific examples of this research:

• "Research on adolescents shows that irregular sleep schedules impair memory consolidation"
  • This is telling us what research on teenagers reveals: when they have irregular sleep schedules, it hurts their ability to consolidate memories.
  • Notice "shows" is present tense - it's presenting what research reveals.

This is where we have the blank:

• "while investigation of adult subjects ______ that even moderate sleep restriction significantly reduces executive function."

Let's look at the choices:

• We're deciding between different verb tenses: will demonstrate (future), demonstrates (present), demonstrated (past), had demonstrated (past perfect).

To see what works here, let's understand what the rest of the sentence is telling us and how it connects to the first part!

The complete second part says:

• "investigation of adult subjects ______ that even moderate sleep restriction significantly reduces executive function"
  • This is presenting what research on adults shows
  • "reduces" is present tense

What do we notice about the structure here?

These two clauses are working in parallel - they're both presenting research findings:

• "Research on adolescents shows..."
  • Subject: "Research" (singular)
  • Verb: "shows" (present tense, singular)
• "while investigation of adult subjects ______..."
  • Subject: "investigation" (singular)
  • Verb: needs to match the parallel structure

Both clauses are connected by "while" and present what current research reveals about different groups. They should use matching verb forms.

Also notice:

• All the other verbs describing what happens are in present tense:
  • "impair" (what irregular sleep schedules do)
  • "reduces" (what sleep restriction does)

These are general research findings presented in present tense.

So we need: demonstrates (Choice B)

• It's singular (matches "investigation")
• It's present tense (matches "shows" and maintains consistency)
• It creates proper parallel structure

Grammar Concept Applied

Maintaining Verb Tense Consistency in Parallel Structures

When two clauses are connected by coordinating words like "while," "and," or "but" and present parallel information, they should use matching verb tenses. This is especially important when both clauses are describing the same type of action or information.

Pattern in this question:

• Clause 1: Research on adolescents shows [present tense]...
• Clause 2: investigation of adult subjects demonstrates [present tense]...

Both clauses present what research reveals, so both use present tense.

Additional examples of parallel verb tense:

Example 1 - Scientific findings (present tense for general truths):

• "Studies on mice indicate that exercise improves cognition, while research on humans suggests similar benefits."
• Both use present tense because both present current research findings

Example 2 - Historical events (past tense for completed actions):

• "The committee reviewed the proposal in March, while the board approved it in April."
• Both use past tense because both describe completed past actions

Example 3 - Subject-verb agreement also matters:

• Singular subject needs singular verb: "investigation demonstrates"
• The word "investigation" is singular, so it needs the singular form "demonstrates," not "demonstrate"

In this question: Since both clauses present general research findings using present tense ("shows," "impair," "reduces"), the verb in the blank must also be present tense. The answer "demonstrates" maintains this consistency while also agreeing with the singular subject "investigation."