Concept:Choose a word that can act as a plural pronoun referring to the countable noun "students."
Explanation:The sentence contrasts two groups of students.
Some may be innocent, and the remaining part is guilty.
The blank must therefore stand for "students" and carry a plural meaning.
Quantifiers like "much," "a great deal," and "a good deal" are used only with uncountable nouns such as "water" or "time."
They cannot modify the plural countable noun "students."
The word "most" works as a plural pronoun meaning "most students."
It fits the contrast perfectly: some are innocent, but most are guilty.
Answer:C. most