An agreement question tests whether a verb matches a subject that's one thing or more than one. Sort the verb forms by whether they work with it or they, rather than by tense. Then ask who or what the verb is about, and find the true subject past any describing phrases. Match singular subjects with singular verbs and plural subjects with plural verbs. Describing words between commas don't change how many things the subject names.
Hints
- Hint 1
Look at the sentence containing the blank and ask what the sentence calls examples of divergent boundaries.
- Hint 2
Set aside the words between the commas, then replace what's left of the subject with it or they. Which pronoun works?
Step-by-step
Sort, find, and match
Step 1Sort the verb forms by number
Start by sorting the verb forms by whether they work with it or they, not by tense. Was and is fit one thing, and has been also fits one thing because its helper, has, is singular. The blank before examples of divergent boundaries needs a main verb, the verb that makes the sentence complete. The true subject decides the verb's number, so we need to find what the sentence calls examples.
- Step 2
Find the subject past the description
What does the sentence call examples? It names The East African Rift and the Mid-Atlantic Ridge, so and joins two places into a plural subject. The words each created by plates pulling apart describe how each place formed, and the commas show that we can set that description aside. Each would take a singular verb if it were the subject, but here it only describes the two places one at a time. Cross out that phrase, and both place names remain as the subject.
- Step 3
Match the subject with they
Try replacing The East African Rift and the Mid-Atlantic Ridge with they, the pronoun for more than one thing. Which choice works after they? The plural form are gives they are examples, so it matches the subject when we put the full place names back into the sentence. Choice B.