An agreement question tests whether a verb matches its true subject, even when that subject is long. Sort the verb forms by whether they go with it or they, then ask what the main verb is about. Read the whole opening to see whether a noun or a full statement answers that question. A whole statement used as the subject counts as one thing, so its main verb is singular. Other nouns inside it don’t decide that verb’s number.
Hints
- Hint 1
Read the full opening before the blank, starting with That. What role does that opening play in the sentence?
- Hint 2
Look at “have persisted” and the blank. Ask what each verb is about.
- Hint 3
Try replacing the full subject with it or they. Which one keeps the sentence’s meaning?
Step-by-step
Find the true subject
Step 1Sort the verb forms
Start by testing the verb forms with it and they because this question asks whether the verb matches its subject, the thing it’s about. The forms have surprised, were surprising, and surprise go with they, so they’re plural. These forms need a plural subject, so we’ll find what the blank’s verb is about rather than decide by tense.
- Step 2
Separate the two verbs
In groups of Wollemi pines have persisted, the groups already have a verb. What does the later blank add? It tells us how something affected conservation biologists, the people affected by it. The blank belongs to the larger sentence, so we need to find the subject of that sentence rather than stop at the groups.
- Step 3
Find what the opening names
Why does That start the sentence? It turns the whole statement about the groups into something the sentence can talk about: the fact that they’ve persisted. We can shrink the opening to that fact without changing what surprised the biologists. The whole opening is the subject, and it names one fact rather than several groups. Plural nouns inside that statement don’t make the fact itself plural.
- Step 4
Match the subject to the verb
Shrink That several genetically distinct groups of Wollemi pines have persisted despite drought and disease to it. We’d say it has surprised conservation biologists, because this one fact takes the singular helper has. Choice C.