A、Close their eyes. B、Fly in circles. C、Hide in dark places. D、Cease moving. D

Have you ever wondered why you see moths flying mostly at night, and then only around lights? It’s evident that moths are attracted to light, but what do you suppose the light does to them? Here’ s my theory. A moth’ s nervous system is extremely sensitive to light. I think that light causes the moth to reduce its movements.
   At night, light hitting one side of a moth is perceived by the moth ’ s eye, stimulating the nervous system. This produces a reflex action that reduces wing movements on the side facing the light. When the wings on that side slow down, the uneven wing beat turns the other side of the moth to the light. In this way, the moth is continually turning near a light. During daylight hours, light is much more intense and evenly distributed, causing the moth to remain motionless.
Q:
18. What is main topic of the passage?
19. What does intense, even light cause moths to do?
20. What can be inferred from the speaker’ s comments about the flight of moths in total darkness?