A.To be on the alert when being followed. B.Not to leave senior citizens alone at home. C.Not to let anyone in without an appointment. D.To watch out for those from the electricity board.

C
C【听前预测】1．两项是todosm．，两项是nottodosth．，可推测该题考查的是要某人做什么事或者不要做什么事。2．两项含有表示警惕的词(Onthealert，watchout)。结论：该题很可能考查对某人的警告或者劝诫。听音重点为0nthealert、leavealone、letin和watchout。【解析】女士在对话中提到，警方提醒人们，尤其是退休在家的老年人，如果没有事先预约过，就不要让任何人进门。故C为正确答案。