It comes from the verb ser.
Ser is the answer.
In this case, it is necessary to remember that the verb be has two different meanings in Spanish. They are: ser and estar. In this case the form of the verb is eres which refers to the subject tú (you in English) in the present tense . Due to this, the first answer is the right one.
Note: "eres" is the conjugation that corresponding to the present tense, second person, singular, subject pronoun, Spanish "tú" (informal version of "you") ;
Note: "eres" ; or "tú eres" ; means: "you are" . The Spanish verb "ser" ; means "to be".
Note that Answer choice: [B]: "estar" ; also, means "to be" ; however this answer choice is incorrect; since "eres" is NOT a conjugation of "estar" .
Note that: "estar" is one type of Spanish verb meaning "to be" and is used in certain situations, whereas the Spanish verb "ser" means "to be" and is used in other situations.