单项选择题
A．in our eyes B．only when we think very hard about something C．only under the direction of a psychologist D．in every person's mind
A．Psychologists do not yet know how people see. B．The experiments in which all factors are controlled are better. C．The study of perception is going on now. D．Perception does not involve psychological factors.
A．they see different things B．some have better eyesight C．they cannot agree about things D．none of these