Answer: The right answer is actually "no estudies."
Explanation: Just to elaborate a little on the answer, it can be added that in this exercise they are asking you to conjugate the so-called imperative mood, which primarily expresses a command, an appeal, or a plea. The negative command of the verb "estudiar" (to study) in the second person singular is "no estudies" and it can be translated as "do not study."
