Los alumnos al profesor. (escuchar) a. escuchan c. escuchamos b. escuchas d. escucho

Right a. escuchan

Since los alumnos can be replaced by ellos, this sentence stands for the third person plural. So escuchan is the conjugation of the regular verb escuchar that matches the subject pronoun ellos. On the other hand, alumnos is a masculine plural noun, hence the matching definite article is los (masculine plural form). Finally:

Los alumnos escuchan al profesor

For this question, it will be important to use the words "mejor" (better), "lo mejor" (the best), and "lo peor" (the worst). while "mejor" is comparative (you are comparing one thing to something else), "lo mejor" and "lo peor" are superlative (there is nothing else better or worse than what these words are describing - there is no comparison).  you could say something like: la música rap es mejor que la música clásica - que es lo peor - pero la música rock es lo mejor de todas las formas de la música (rap music is better than classical music - which is the worst - but rock music is the best out of all the forms of music).