(A) is mentioned at the end of P2. But it’s mentioned as part of a discussion of how situational factors affect code-switching. It doesn’t provide evidence that some code-switching is explained by non-situational factors.

Used as evidence that code-switching is sometimes based on non-situational factors. A “domain” is defined earlier to refer to a mix of situational factors. If the domain would lead one not to expect code-switching, that means the mix of situational factors would lead one to believe the participants would stick only to one language. But even in some of these cases, code-switching occurs, as shown in P3.

Not used as evidence that code-switching can’t be entirely explained by situational factors. In P2, we learn that situational factors can lead people to use a mix of languages. This isn’t presented as evidence that sometimes we need to turn to non-situational factors to explain code-switching. Some contexts, even if they don’t change, might lead to mixed use of Spanish and English. This is entirely consistent with situational factors as an explanation for code-switching in those situations.

(D) sounds very similar to what’s described in P3. But the family in P3 mainly used English at home. Although we know that the situational factors would lead us to believe the family doesn’t code-switch, that doesn’t imply we’d expect the family to use Spanish as the primary language instead of English as the primary langauge. Because (D) isn’t something mentioned in the passage, it isn’t used to support the claim that code-switching can’t be entirely explained by situational factors.

Although P3 notes that sometimes people are unaware of their code-switching, the author never discusses lack of awareness of which situational factors can influence choice of language. Since (E) isn’t mentioned, it’s not used by the author to show that code-switching can’t be entirely explained by situational factors.