In her groundbreaking 2019 study, marine biologist Dr. Elena Rodriguez tracked migration patterns of humpback whales across the Pacific Ocean....

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 her groundbreaking 2019 study,
  • marine biologist Dr. Elena Rodriguez
    • tracked migration patterns
      • of humpback whales
        • across the Pacific Ocean.
• Documenting the precise routes and feeding behaviors
  • of these endangered mammals
• [?] essential
  • to Rodriguez's research,
    • which later informed international conservation policies.

Understanding the Meaning

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

• 'In her groundbreaking 2019 study, marine biologist Dr. Elena Rodriguez tracked migration patterns of humpback whales across the Pacific Ocean.'
  • This tells us about a study from 2019 where Dr. Rodriguez followed and recorded how humpback whales moved across the Pacific.
  • The time frame is past (2019).

Now the second sentence begins:

• 'Documenting the precise routes and feeding behaviors of these endangered mammals...'
  • This is talking about the act of recording exactly where the whales went and how they fed.

This is where we have the blank.

Let's look at the choices:

• were (plural, past)
• was (singular, past)
• are (plural, present)
• have been (present perfect)

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

The sentence continues: '_____ essential to Rodriguez's research, which later informed international conservation policies.'

So the complete sentence is telling us:

• Documenting these precise routes and behaviors was essential to Rodriguez's research.
• That research then helped shape international conservation policies.

What do we notice about the structure here?

• 'Documenting the precise routes and feeding behaviors of these endangered mammals' is the subject of the sentence.
  • Even though this phrase contains plural words like "routes," "behaviors," and "mammals," the subject itself is the single act of documenting.
  • When a verb ending in -ing acts as a noun (like "documenting" here), it's always treated as singular.
  • Think of it like: "Swimming is fun" (not "are fun") or "Reading books takes time" (not "take time").
• We also need past tense:
  • The study happened in 2019.
  • The research "informed" policies (past tense).
  • Everything described is in the past.

So we need a singular, past tense verb: was

GRAMMAR CONCEPT APPLIED

Subject-Verb Agreement with -ing Verb Forms Used as Nouns

When a verb ending in -ing acts as a noun (called a gerund in grammar terms) and serves as the subject of a sentence, it's always treated as singular, even if it contains plural nouns within its phrase.

Pattern:

• Singular: Documenting the routes was essential (not "were")
• Singular: Collecting rare coins requires patience (not "require")
• Singular: Reading these books takes time (not "take")

Why this matters:

• The subject is the action itself (one action = singular)
• "Documenting" = the act of documenting (singular)
• "routes," "behaviors," "mammals" are objects within the phrase, not the subject

In this question:

• Subject: "Documenting the precise routes and feeding behaviors of these endangered mammals"
• This is one action (documenting), so it needs a singular verb
• The time frame (2019 study) requires past tense
• Therefore: was