Which statement is true about the verb estar?

a.
it is an irregular verb.

b.
its yo form follows a regular pattern.

c.
it is a regular verb.

d.
its yo form needs an accent mark.

It is Irregular:
 Spanish verbs are composed of a stem and root (-ar, -er and -ir)
Some IRREGULAR VERBS change their stem in the present tense,indicative mode.
when a VERB is conjugated, and E is the last stem vowel, and it's stressed, e changes to ie

Amí y a mis amigos les gusta ir al parque. solíamos ir todo el tiempo, pero ahora no vamos tanto. mi familia y yo celebramos fiestas durante las vacaciones. en mi tiempo libre me gusta ir en monopatín y me gusta andar en bicicleta. here you go : )