GRE Reading Comprehension: ETS Official Practice 150-GRE OP150: 阅读 - YA92C7Q1H4S303HO1

The plant called the scarlet gilia can have either red or white flowers. It had long been thought that hummingbirds, which forage by day, pollinate its red flowers and that hawkmoths, which forage at night, pollinate its white flowers. To try to show that this pattern of pollination by colors exists, scientists recently covered some scarlet gilia flowers only at night and others only by day: plants with red flowers covered at night became pollinated; plants with white flowers covered by day became pollinated.