Marine biologists have long observed that coral reefs support extraordinary biodiversity, with some ecosystems containing thousands of distinct specie...

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:

• Marine biologists have long observed
  • that coral reefs support extraordinary biodiversity,
    • with some ecosystems containing thousands of distinct species in relatively small areas.

Sentence 2:

• Recent studies [?]
  • that these underwater habitats may harbor even more genetic diversity than previously estimated,
    • with implications for conservation strategies worldwide.

Understanding the Meaning

Let's start with the first sentence to get context:

• 'Marine biologists have long observed that coral reefs support extraordinary biodiversity'
  • Scientists who study ocean life have known for a while that coral reefs have incredible variety of life
• 'with some ecosystems containing thousands of distinct species in relatively small areas'
  • These reefs can pack thousands of different species into fairly compact spaces

Now the second sentence begins:

• 'Recent studies...'

Here's where we have the blank. Let's look at our choices:

• A. having suggested
• B. to suggest
• C. suggest
• D. suggesting

We're deciding what verb form follows 'Recent studies.'

What do we have so far?

• 'Recent studies' is our subject - it's plural
• We need a verb to tell us what these studies do
• The structure is: 'Recent studies [verb] that...'

This is a straightforward subject + verb setup. 'Recent studies' needs a main verb to complete the sentence.

So we need: suggest - the simple present tense form that matches the plural subject 'studies.'

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

• 'that these underwater habitats may harbor even more genetic diversity than previously estimated'
  • The studies are showing that coral reefs might have even more genetic variety than scientists originally thought
• 'with implications for conservation strategies worldwide'
  • This finding matters for how we protect these ecosystems around the world

What do we notice about the structure here?

• 'Recent studies' is the subject doing the main action
  • It's plural, so we need a plural verb form
• The sentence needs a main verb - one that can stand on its own
  • 'Suggest' is a complete, finite verb that works with 'studies'
  • It naturally takes a 'that' clause as its object

The correct answer is C. suggest - it provides the main verb the sentence needs and agrees with the plural subject.

GRAMMAR CONCEPT APPLIED

Using Finite Verbs as Main Verbs

Every complete sentence needs a finite main verb - a verb form that can stand on its own and show tense. The main verb must agree with its subject in number (singular/plural).

Finite verbs vs. Non-finite verbs:

Finite verbs (CAN be main verbs):

• Simple present: 'Studies suggest...'
• Simple past: 'Studies suggested...'
• Present perfect: 'Studies have suggested...'

Non-finite verbs (CANNOT be main verbs alone):

• Infinitives: 'Studies to suggest...'
• Present participles: 'Studies suggesting...'
• Perfect participles: 'Studies having suggested...'

In our question:

• Subject: 'Recent studies' (plural)
• Need: A finite verb that agrees with plural subject
• Answer: 'suggest' (simple present, plural form)
• Result: 'Recent studies suggest that...'

The non-finite forms (infinitives and participles, called verbals in grammar terms) can serve other functions in sentences - as modifiers, parts of verb phrases with helping verbs, or in dependent clauses - but they cannot stand alone as the main verb of a sentence.