An agreement question tests whether a verb matches its subject, the person or thing it’s about. Sort the forms using it for one thing and they for more than one. If the blank sits inside extra information, find the subject of that part rather than borrowing the main subject. One thing takes a singular verb; more than one takes a plural verb. Nearby nouns don’t decide agreement unless they’re the subject.
Hints
- Hint 1
Read the words between the commas on their own. The missing verb belongs to that part of the sentence.
- Hint 2
Look at the phrase right before the blank. Which word is the subject, and which words tell you the group it comes from?
- Hint 3
Test that subject with it or they. Does it name one thing or more than one?
Step-by-step
Sort, find the true subject, and match
Step 1Sort the verb forms
The choices use forms of be, so let’s sort them by number rather than tense. Do they fit it or they? The forms are, have been, and were fit they, so they’re plural. Since the blank comes before meticulously cataloged, we need to find what is cataloged and decide whether its subject is one thing or more than one.
- Step 2
Find the verb’s own part
Which part of the sentence needs this verb? The sentence starts with The staggering number of satellite images, and has enabled researchers tells us what that number has done. The blank belongs to the extra information between the commas, which says how the images are prepared for release. We need the subject inside that extra information, because this verb describes the images, not what enabled the research.
- Step 3
Separate the subject from its group
What is being cataloged: the whole group together, or each image on its own? In each of which, which refers to all the satellite images, but of which only tells us the group each image belongs to. Set that phrase aside, and each is left as the subject. The subject each means each one, taken alone, so it counts as one thing even though there are many images.
- Step 4
Use the singular form
Replace the subject with it: it is meticulously cataloged. The form is matches one thing, so it completes the verb about each image being cataloged before release. Choice A.