An agreement question tests whether a verb matches its subject in number: one thing or more than one. Sort the verb forms by whether they work with it or they, then find the true subject. An of phrase can hold extra nouns, so set that phrase aside and ask who or what the verb describes. One thing takes a singular verb, and more than one takes a plural verb. A nearby noun doesn’t decide the verb’s number unless it’s the subject.
Hints
- Hint 1
Look at the full phrase before the blank. Which word names the subject, and which words describe the group it comes from?
- Hint 2
Cross out the phrases that start with of, then try it or they in place of the subject. Which pronoun matches what’s left?
Step-by-step
Sort, find the subject, and match
Step 1Sort by number
The blank comes before its ability to survive without drinking liquid water. What does it need to do? It needs a verb linking the subject to that ability, so start by sorting the forms by number. The forms are, have been, and were all work with they, which means they’re plural forms.
- Step 2
Find the true subject
What is being described as the ability to survive without drinking water? Start with One of the most useful adaptations of the desert kangaroo rat, and cross out the phrases beginning with of. The phrase about adaptations tells us the group, and the phrase about the kangaroo rat tells us whose adaptations they are. What’s left as the true subject is one adaptation, not the whole group.
- Step 3
Check with a pronoun
Replace One with it to check the verb. Which form can follow it? We say it is, so the singular form is matches this subject and links it to the ability named after the blank. Choice D.