Question 140·Medium·Form, Structure, and Sense
Crows are highly intelligent birds, and one of the most striking behaviors ______ the ability to recognize human faces and convey warning calls about individual people to their flock.
Which choice completes the text so that it conforms to the conventions of Standard English?
For subject-verb agreement questions, first isolate the true subject of the verb—ignore prepositional phrases like "of the most striking behaviors" and focus on the main noun (here, "one"). Decide if that subject is singular or plural, then quickly eliminate any verb choices that don’t match in number. Next, check the tense: ask whether the sentence describes a general truth (usually present tense) or a specific past event (past tense). Finally, make sure the choice works as a complete main verb in the sentence, not just as a fragment or participle.
Hints
Locate the true subject
Focus on the phrase "one of the most striking behaviors". Which word in that phrase is actually the subject that the verb should agree with?
Match singular or plural
Once you know whether the subject is singular or plural, compare it to the verb forms in the options and remove those that don’t match in number.
Consider the time being described
Is the sentence describing a one-time event in the past, or a general truth about crows that is still true now? Use that to decide which verb tense fits best.
Check for complete verb form
Make sure the word you choose can serve as the main verb of the clause on its own, without needing extra words to complete it.
Step-by-step Explanation
Identify the subject of the verb
Look closely at the phrase before the blank: "one of the most striking behaviors". The head noun here is "one", not "behaviors". That means the subject of the verb is singular.
Decide on singular vs. plural verb
Because the subject is singular ("one"), the verb that fills the blank must also be singular, not plural. So any verb form that is only used with a plural subject will be wrong here.
Check the time (tense) of the sentence
The sentence is describing something that is generally true about crows, not something that happened only in the past. General facts are usually stated in the present tense, not past tense.
Eliminate choices that don’t match number or tense
Choice A, "was," is singular but past tense, which does not match a general, timeless fact. Choice B, "are," is present tense but plural, which does not match the singular subject "one." Choice D, "being," is not a complete main verb here and would make the sentence ungrammatical. The only choice that is both singular and present tense, and works as a complete main verb, is C) is.