Concept:The subject “One” is singular, so it needs a singular verb.
Explanation:The phrase “One of the clever pupils” means “one pupil among many”.
Because the subject is “One”, not “pupils”, the verb must be singular.
“Can” cannot be used with “able” because it creates a double modal error.
“Were” and “are” are plural verbs and do not match the singular subject.
“Was” is the correct singular past verb that fits the sentence.
Answer:One of the clever pupils
was able to solve the problem.
Correct option: B. was.