单选题 The lady in this strange-tale very obviously suffers from a serious mental illness. Her plot against a completely innocent old man is a dear sign of ______.

【正确答案】 B
【答案解析】insanity精神错乱，精神失常；十分愚蠢的行为；荒唐的行为。impulse突如其来的念头；推动，冲力。inspiration灵感；鼓动人心的人(事)。disposition气质；天性，性格；倾向。