答案：A

解析：

Choice A is the best answer. Miss Grey's observations of her new charges suggests that she thinks the Bloomfield children receive different levels of encouragement. Miss Grey mentions that Mrs. Bloomfield has spoken "such a favourable character" of Tom. Mary Ann, on the other hand, has an "affected simper," or a deliberate and exaggerated ingratiating manner, and a "craving for notice." Overall, it seems Tom receives frequent attention and encouragement while Mary Ann strives for but doesn't always receive supportive attention.