A verb form question tests whether a verb completes a sentence and matches its subject. Sort the choices: an -ing or to form can’t be a main verb on its own. Then read to the period to find which subject still needs a main verb. A subject can contain verbs of its own, so follow the whole subject. In the present tense, one thing takes a verb ending in -s; more than one takes the form without it.
Hints
- Hint 1
Start after the comma following archive and find where the subject ends. How much of the sentence names what’s being called a challenge?
- Hint 2
Ask which subject each verb belongs to. Check identify, refer, and are, including the words after the blank.
- Hint 3
Replace the full subject with it or they. Which pronoun keeps the sentence’s meaning?
Step-by-step
Find the main verb, then match its subject
Step 1Find what the sentence is about
Set aside During the authentication of a newly recovered archive, which tells us when this happens. What is the sentence about? whether the initials begins a question that continues to the blank, and that whole question is the subject. We need its main verb, the verb that says what that question does or is.
- Step 2
Check where the existing verbs belong
Which subjects do the other verbs belong to? Identify and refer belong to the initials beneath several unsigned sketches inside the whether clause, a group of words with its own subject and verb. Later, the relevant ownership records are incomplete has are, but since makes that part explain why the issue is difficult. None says what the whole question does or is, so the blank must supply its main verb.
- Step 3
Set aside forms that can’t be main verbs
To pose and posing can’t supply that main verb before a challenge for conservators. A to form can’t be a main verb on its own, and an -ing form needs a helper such as is. Either would leave a fragment, words that can’t stand alone as a sentence.
- Step 4
Match the subject’s number
Does the subject name several initials or one question about who they identify? The whole stretch beginning whether the initials names one question, so the subject is singular. Replace it with it: it poses a challenge uses the singular present-tense form, while it pose doesn’t. Choice D.