For this case we can translate the question as:
What is the official language of Spain?
By definition, we have to:
In Spain several vernacular languages are spoken. Spanish is the official language throughout the country, it is the predominant mother tongue in almost all the autonomous communities of Spain. Six of the seventeen autonomous communities of Spain also have, together with Spanish, other languages as co-officers.
Answer:
OPTION A
EL castellano (Español)