For subject-verb agreement questions with long subjects, ignore prepositional phrases, relative clauses, and interrupting expressions such as “together with.” Reduce the sentence to its subject and main verb, identify the subject's head noun, and then choose the verb form that agrees with that noun rather than with the closest noun.
Hints
- Hint 1
Find the sentence's core
Temporarily remove the phrases between the subject and the blank. What single noun is performing the action of explaining?
- Hint 2
Examine the connecting phrase
Consider whether “together with” makes the subject compound in the same way that “and” would.
- Hint 3
Check agreement
Select the verb form that agrees in number with the head noun of the complete subject, not with a nearby noun.
Step-by-step
- Step 1
Identify the main subject
Set aside the modifiers to reveal the sentence's core structure: “The persistence ______ why a memory may feel increasingly reliable.” The head noun of the subject is the singular noun “persistence.”
- Step 2
Evaluate the added phrase
The phrase “together with the confidence those images inspire” provides additional information about persistence. Unlike a phrase using “and,” a phrase beginning with “together with” does not create a compound subject.
- Step 3
Match the verb to the subject
Because “persistence” is singular, the main verb must also be singular. Therefore, “helps explain” completes the sentence correctly.