Marine biologists studying biodiversity patterns have identified distinct population dynamics in various aquatic environments. Between 2000 and 2020, ...

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

• Marine biologists studying biodiversity patterns
• have identified distinct population dynamics
• in various aquatic environments.

• Between 2000 and 2020,
• [?] species diversity levels
• showed contrasting trends,
• with reef environments demonstrating increased diversity
• while estuary environments showed gradual decline.

Understanding the Meaning

Let's start reading from the beginning to understand what this passage is telling us.

The first sentence gives us the context:

• Marine biologists studying biodiversity patterns have identified distinct population dynamics in various aquatic environments.
  • Scientists studying life diversity in water have found different population patterns in different types of water environments.

Now the second sentence:

• Between 2000 and 2020...
  • This gives us the time period being studied.

This is where we have the blank:

• [blank] species diversity levels showed contrasting trends

Let's look at the choices:

• A: reefs and estuaries
• B: reef and estuaries
• C: reef's and estuary's
• D: reef and estuary's

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

The sentence continues:

• "with reef environments demonstrating increased diversity while estuary environments showed gradual decline"
  • Reef environments showed MORE diversity
  • Estuary environments showed LESS diversity
  • These are opposite trends

Now let's understand the relationship in the blank:

• We have "[blank] species diversity levels"
• The sentence is talking about the diversity levels that BELONG TO or are ASSOCIATED WITH reef environments and estuary environments
• It's really saying "the reef's species diversity levels" and "the estuary's species diversity levels"

What do we notice about the structure here?

• The diversity levels belong to these environments
• When we want to show that something belongs to or is associated with something else, we need possessive forms
• Just like we'd say "the dog's bone" (not "dog bone" when we mean the bone belonging to the dog)

So we need: reef's and estuary's (both possessive forms to show the diversity levels belong to/are associated with these environments).

The correct answer is C.

GRAMMAR CONCEPT APPLIED

Using Possessive Forms to Show Belonging or Association

When you want to show that something belongs to or is associated with a noun, you use the possessive form by adding an apostrophe + s (called the possessive apostrophe in grammar terms):

Basic pattern:

• Without possession: dog collar → sounds like a type of collar
• With possession: dog's collar → the collar belonging to the dog

For singular nouns: Add 's

• the reef's species diversity levels = the species diversity levels associated with the reef
• the estuary's species diversity levels = the species diversity levels associated with the estuary

In compound expressions: Each noun that has something belonging to it needs the possessive form:

• Incorrect: "The teacher and student's books showed up" (sounds like shared books)
• Correct: "The teacher's and student's books showed up" (each has their own books)

How it applies to our question:

• We're discussing diversity levels that belong to/are associated with TWO different environments
• Each environment has its own diversity levels
• So both need possessive forms: "reef's and estuary's species diversity levels"
• This makes it clear we're talking about the diversity levels OF these environments