Right answer:
¿Esperan el autobús los estudiantes?
¿Esperan los estudiantes el autobús?
We can write this sentence in two ways as established above. Thus, in this sentence we have two subjects. First of all, los estudiantes and then el autobús. We have inverted the word order and the sentences are correct. So autobús means bus and estudiantes means students. Moreover, esperan is the conjugation of the verb esperar for the third person plural in the simple present.