A verb form question tests whether a blank needs a main verb and whether it matches the subject. Sort the forms: an -ing or to form can't be a main verb alone. Find the subject, set aside extra phrases and their verbs, and read to the period. With no main verb, the blank must supply one. Then check the subject as it or they: one thing takes a singular verb, and more than one takes a plural verb.
Hints
- Hint 1
Read the second sentence through to its period and look for its subject and main verb.
- Hint 2
In the words between commas, check which noun goes with accounts. Does that verb belong to the whole sentence or to the part starting with that?
- Hint 3
Set aside the words beginning with between and the words between commas. Decide whether the subject left is one thing or more than one.
Step-by-step
Count the main verbs, then match the subject
Step 1Sort the forms and read through
Sort the choices by what they can do: revealing and to reveal can't be main verbs on their own. A main verb tells what the subject does or is, and the subject is who or what the sentence is about. Does this sentence already have a main verb? Start with The discrepancies and read to the period, checking whether any verb already belongs to that subject.
- Step 2
Separate the model's verb from the sentence's verb
Can that accounts for the effects of temperature and pressure on rock supply that main verb? No, accounts tells what the model does. It belongs to the that clause, a group with its own subject and verb. Set aside the whole section beginning with together with a computer model, since it's extra information between commas. The words after the blank name the outline but supply no verb, so the blank needs a main verb for the discrepancies. Revealing and to reveal can't supply one, so each would leave a fragment, words that can't stand alone as a sentence.
- Step 3
Match the plural subject
Which words decide the verb's number? In The discrepancies between the waves' expected arrival times and their observed arrival times, the subject is discrepancies; the words beginning with between tell us which differences are meant. The phrase together with a computer model adds extra information, but unlike and, it doesn't join a second subject. Because the discrepancies are plural, use reveal, as in they reveal; reveals would fit the singular it. Choice A.