TOEFL Reading: ETS-TOEFL阅读机经 - K6T2H83FC5E4UHH4L$

According to paragraph 1, what is the phi phenomenon? A. The appearance of movement that occurs when one light is turned off while another lights up nearby B. The tendency to see two lights placed close together as coming from a single light source C. The fact that the human eye sees a light source for a split second after it has disappeared D. The impression that there are several light sources when there is actually only one