It would be the 3rd one, hacia
1. A mi madre le encanta pasear en bicicleta.
This sentence means - My mother loves riding her bicycle. Here, you have to use the pronoun LE because it is the indirect object pronoun for third person singular, which is he and she (el y ella). If you used ME encanta, that would mean - I love, and here you have to show that your mom loves something.
2. A ellos les interesa la historia.
This sentence means - They are interested in history. Here, you have to use the pronoun ELLOS because of the pronoun which follows it - LES. Les refers to third person plural, which in this case is ELLOS. Nosotros means - we.
3. A ustedes les encanta viajar. Este ano visitaron seis estados!
This sentence means - You love traveling. This year you visited six countries! Here you have to use the phrase LES ENCANTA because it means - you love. Les aburre means quite the opposite - it would mean that they are bored, which they clearly are not.
4. A ti te importan los deportes?
This sentence means - Are you interested in sports? This one is a bit tricky to explain - you have to use the plural form of the verb (importan instead of importa) because the verb refers to the object (los deportes) which is plural, rather than the subject (tu) which is singular.
5. A Daniela y a mi nos fascina la literatura.
This sentence means - Daniela and I are fascinated by literature. Here, you have to use the pronoun NOS because it means - we. Given that you are also included here (Daniela and I), you cannot use the pronoun les which refers to they, rather than us.
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."
