A verb agreement question tests whether a verb matches its subject, singular or plural. First, sort the verb forms by number using it for one thing and they for more than one. Then cross out phrases and extra words between commas and ask who or what the verb is about. A singular subject needs a singular verb, and a plural subject needs a plural verb. The nearest noun doesn't decide the verb unless it's the subject.
Hints
- Hint 1
Focus on the second sentence. Ask what is helping researchers identify pollution sources.
- Hint 2
Set aside the words between commas and the phrase beginning with from. What part of the sentence is left to do the helping?
- Hint 3
Try replacing that subject with it or they. Which pronoun stands for the whole subject?
Step-by-step
Find the true subject and check its number
Step 1Connect the verb to its subject
Read helping researchers identify possible sources of pollution to see what the verb describes. We need to find what is helping the researchers, because the verb must agree with that subject. A subject is who or what a verb is about, and its number tells us whether the verb needs a singular or plural form.
- Step 2
Remove the words hiding the subject
What is helping the researchers: the readings, the sites, or the station? Cross out from the upstream site and the downstream site, which tells us where the readings come from. Also cross out each recorded by a separate monitoring station, which tells us how they're recorded. That leaves "The readings" as the true subject, the word that tells us what does the helping. The word and joins the two sites inside the from phrase, so those sites aren't separate subjects. Each describes the readings one at a time, but it's in extra words and doesn't change their number.
- Step 3
Use the pronoun check
Replace "The readings" with a pronoun: does it or they stand for more than one reading? The short sentence is they are helping, so are is the form that agrees with this subject. Is, was, and has been need a singular subject and can't pass the they check. Choice B.