"A student who submits a research paper with a weak thesis and multiple sources is going to receive a higher grade than students who submit a research paper with a powerful thesis and only a less sources. "
This sentence has the correct subject-verb agreement.
Answer: A
Explanation
When dealing with sentences of subject-verb agreement, there are few rules to keep in mind.
Accordingly, if the subject is singular or plural, the verb must match the subject by being singular or plural respectively.
Therefore 'A student' ties with 'submits' as the verb being singular and 'students' ties with 'submit;' verb being plural.