To best answer this question, we must first clarify what an intensive pronoun is.
Intensive pronouns are reflexive pronoun used to add emphasis to a sentence. As a result, an intensive pronoun is not necessary to the meaning of the sentence. Intensive pronouns are the same as reflexive pronouns: myself, yourself, himself, herself, itself, ourselves, yourselves, themselves.
Every sentence given above contains reflexive pronouns, but not all of them are intensive pronouns.
In the first sentence, "herself" is a reflexive pronoun. However, it IS essential to the meaning of the sentence. Talking to herself is different than talking to others. Therefore, sentence A. does NOT contain an intensive pronoun.
In the second sentence, "myself" is NOT essential to the meaning of the sentence. If the word "myself' were eliminated from the sentence, the meaning of the sentence would remain the same. There, sentence B. does contain an intensive pronoun.
In the third sentence, the word "themselves" is essential to the meaning of the sentence. If the word "themselves" were eliminated, the meaning of the sentence would not remain the same, because we need to know they went alone (as opposed to going with their parents). As a result, sentence C. does NOT contain an intensive pronoun.
Finally, in the fourth sentence, the word "himself" is necessary to the sentence so that the reader knows just WHO Andy is looking at in the mirror. If this pronoun were removed, the meaning of the sentence would change. As a result, sentence D. does NOT contain an intensive pronoun.
Therefore, the sentence that contains an intensive pronoun is B.
