We can conjugate the verb ''Gustar'' as follows:
- Yo gusta, tú gustas, él gusta, nosotros gustamos, ellos gustan
Verb Conjugation for "gustar"
We know the verb to be because it is known by the pronouns, being: I, YOU, HE, SHE, IT, WE, YOU and They. The basic information of the conjunction of some word - are these pronouns.
The verb ''gustar'' is in the Present Indicative. Therefore, the pronouns with the conjunctions in Spanish, will be:
- yo gusto
- tú gustas
- él/ella gusta
- nosotros/as gustamos
- vosotros/as gustáis
- ellos/ellas gustan
Looking at the alternatives, the most that fits with the most certain conjunction is:
- Yo gusta, tú gustas, él gusta, nosotros gustamos, ellos gustan.
Therefore, the correct option is the letter ''a''