Right answer:
c. abre
La biblioteca abre a las 8:00 de la mañana
Abre is the conjugation of the verb abrir for the first person singular in the simple present. The simple present tense is used to talk about habitual actions or routines. This tense is also used to describe things that happen now or in the near future. So, in this sentence we know that the library always opens at 8:00 in the morning making this a routine.