Final answer:
Mrs. Slade wrote the note addressed to Mrs. Ansley in the context described. Hence the correct option is (a).
Step-by-step explanation:
The note addressed to Mrs. Ansley was written by Mrs. Slade. In the context of this question, it appears to reference a story where one character sends a note to another, and the answer to who wrote it is Mrs. Slade. This type of question typically relates to the analysis of literature where understanding the dynamics between characters is essential.