In the coastal waters of the Great Barrier Reef, colonies of hard coral _______ intricate calcium carbonate structures that provide...

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

• In the coastal waters of the Great Barrier Reef,
  • colonies
    • of hard coral
  • [?] intricate calcium carbonate structures
    • that provide essential habitat
      • for thousands of marine species.

Understanding the Meaning

Let's start reading from the beginning:

'In the coastal waters of the Great Barrier Reef'

• This tells us the location - where this is happening.

'colonies of hard coral'

• This is what the sentence is about.
• Now, what exactly is the subject here?
  • The main word is 'colonies' - that's plural.
  • 'of hard coral' is a describing phrase that tells us what kind of colonies we're talking about.
• So our subject is 'colonies' (plural), not 'coral.'

Now here's where we need to fill in the blank:
'colonies of hard coral ______ intricate calcium carbonate structures'

Let's look at our choices:

• A. constructs - singular verb
• B. construct - plural verb
• C. has constructed - singular verb
• D. is constructing - singular verb

What do we need here?

• Our subject is 'colonies' - which is plural.
• We need a verb that matches a plural subject.
• Only 'construct' is plural.

So we need B. construct.

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

'that provide essential habitat for thousands of marine species'

• This part describes what these calcium carbonate structures do - they provide homes for lots of marine life.

The complete meaning:

• In the Great Barrier Reef's coastal waters, groups of hard coral build complex calcium carbonate structures, and these structures serve as essential homes for thousands of marine species.

What do we notice about the structure?

• The word 'coral' sits between our subject 'colonies' and the verb.
• But 'coral' is just part of a describing phrase ('of hard coral').
• The verb needs to match 'colonies' (plural), not 'coral' (singular).
• That's why we need 'construct' - the plural form.

GRAMMAR CONCEPT APPLIED

Subject-Verb Agreement with Intervening Phrases

When a describing phrase (called a prepositional phrase in grammar terms) comes between the subject and verb, the verb must still agree with the actual subject, not with words in the describing phrase:

The pattern:

• Subject + describing phrase + Verb
• The verb matches the subject in number (singular or plural)

Example 1:

• The boxes of equipment arrive tomorrow.
• Subject: "boxes" (plural)
• Describing phrase: "of equipment"
• Verb: "arrive" (plural) ✓

Example 2:

• The leader of the protests speaks at noon.
• Subject: "leader" (singular)
• Describing phrase: "of the protests"
• Verb: "speaks" (singular) ✓

In our question:

• Subject: "colonies" (plural)
• Describing phrase: "of hard coral"
• Verb needed: "construct" (plural) ✓

The key is to identify the true subject and not be distracted by nouns that appear closer to the verb but are actually just part of a describing phrase.