An agreement question tests whether a verb matches its subject, the person or thing it's about. Sort the choices by number: one thing takes a singular verb, and more than one takes a plural verb. Then read the words around the blank and ask who or what the verb is about. Words between commas can add details without joining the subject, so find the true subject and test it with it or they. The closest noun doesn't always decide the verb's form.
Hints
- Hint 1
The blank comes after the words determined that. Ask what is able to operate for more than two hours.
- Hint 2
Look at the phrase between the commas. Try reading without that phrase, then test the remaining subject with it or they.
Step-by-step
Find the true subject
Step 1Sort the verb forms
Test are, were, and have been with they: all three fit, so they're plural forms, for more than one thing. Sort by number first, because this question needs a verb that matches whatever is able to operate. We can check tense after finding the true subject. A noun's place next to the blank doesn't make it the subject.
- Step 2
Remove the extra phrase
What could operate for more than two hours? Cross out along with its spare batteries, the extra information between the commas, and we're left with the prototype drone. The words along with tell us what comes with the drone; they don't join two subjects as and would. The drone is the true subject, because the sentence reports what that drone could do.
- Step 3
Match the subject
A drone is one thing, so test the verb with it. Which form works? It was able to operate uses the singular form was, which matches the prototype drone and completes the team's report. Choice C.