An agreement question tests whether a verb matches its subject, even when that subject is long. First find the true subject: who or what is the verb about, a noun or a whole activity? Check both verb form and agreement. A main verb shows tense, alone or with a helper; an -ing form needs a helper. A singular subject takes a singular verb, and a plural subject takes a plural verb. Test the whole subject with it or they, rather than matching the nearest noun.
Hints
- Hint 1
Read the last sentence through the period, and check whether the sentence already has a main verb for the full subject. Which words belong to the part that starts with whether?
- Hint 2
Ask what the sentence calls a central goal of the project. Look for the full subject, not a noun inside it.
- Hint 3
Replace the full subject with it or they. Which pronoun fits what the sentence calls a central goal?
Step-by-step
Find the true subject
Step 1Find the blank’s job
Let’s read from Determining whether to the period: does the last sentence already have a main verb that says what its full subject does or is? explained the whales’ altered route belongs to the part starting with whether, and no main verb follows the blank. So the blank needs a main verb, and being can’t supply one without a helper such as is.
- Step 2
Find what counts as the subject
What does the sentence call a central goal of the project? The goal is determining which factor best explained the route change, so the true subject starts with Determining and runs all the way to the blank. The whether clause has its own subject and verb, and it sits inside that full subject. Its list, water temperature, food availability, or shipping noise, names possible causes, not separate subjects for the blank. The whole -ing phrase names one activity, so the true subject is singular.
- Step 3
Match the verb to the whole activity
Shorten the whole subject to it, then test the remaining main-verb forms. Both were and have been are plural forms, so they work with they, not it. The time clue In 2023 sets the project in the past, so the singular past form was completes the sentence: it was a central goal. Choice A.