Students is a countable noun, "much" is used for uncountable nouns. Thus, we are left with the first three options. "A few" and "some" signify the same thing. When we try to understand the difference between "a few" and "few". Few is used to define a very small amount of something, whereas "a few" is used when it is more than the small amount but not a lot of it is there. Thus, Option B and C almost means the same thing. We cannot have two options as answer. Option A is the correct answer.