An agreement question tests whether a verb matches its true subject, even in an unusual word order. Sort the forms by number: one thing works with it, and more than one works with they. Set apart forms that can’t be a main verb on their own. Then ask who or what the verb says something about, looking past phrases that describe other nouns. If the subject follows the verb, flip the sentence to check the match.
Hints
- Hint 1
Start at the semicolon and check for a main verb in that part of the sentence. Which words belong to the clause beginning with that?
- Hint 2
Trace where the opening phrase ends by reading from among through the words describing the patterns. Then look on both sides of the blank for who or what the verb is about.
- Hint 3
Try flipping the word order to put the subject before the verb. Which words name who or what the verb is about, and which noun decides whether it’s one thing or more than one?
Step-by-step
Find the subject after the verb
Step 1Sort the verb forms
Sort the forms of be by number and whether they can be a main verb, the verb that says what a subject does or is. Are and were are plural, while having been can’t be a main verb on its own. Does have documented already fill that role after the semicolon?
- Step 2
Separate the describing clauses
Which part does that researcher Leena Saar and her colleagues have documented describe? It describes the geographically distinctive patterns, so its verb belongs to that describing clause, a group with its own subject and verb. Later, were built belongs to the clause about the vessels. Neither is the main verb for the part beginning with among, so the blank needs one.
- Step 3
Flip the word order
The opening among phrase tells where something belongs, but it doesn’t name that something. What is among those patterns? Read past for example to a cluster of unusually narrow rings, and flip the order: the cluster ___ among those documented patterns. The subject comes after the verb, and cluster names one group. The words after cluster tell us what the group contains, so the many rings don’t make the subject plural.
- Step 4
Match the singular subject
Replace a cluster with it to check the verb’s number. Which form works with that pronoun? We say it is, so is is the singular main verb that completes this sentence about the cluster. Choice D.