Which statement is correct about the brain of bilingual and multilingual?

Which statement is correct about the brain of bilingual and multilingual?

a) The learning of sign language as a second language follows the same principle as the learning of a verbal second language Ob) As older we are when we start learning a second language, the less language proficient we will become in the second language od The temporal cortex stores the different languages separately from one another and controls the switching between the languages All of the above Only a) and b)