Young sunflowers face the sun as it rises in the east and follow it across the sky until it sets in the west. Why does this happen? A team of scientists has finally been able to figure____ how and why young sunflowers move.

    Older sunflowers always face east. However, as it____(turn) out, an internal（内部的）clock helps young sunflowers track the sun so that they can grow better. US biologist Stacey Harmer and her colleagues had it____(explain) in a recent paper published in the journal Science on Aug. 5.

    ____(depend) on the time of day, certain growth genes seem to work to different degrees on different____(side) of young sunflowers' stems（茎）. The east side of their stems grows faster during____day, causing the stems to ____(gradual) bend from east to west. The west side grows faster at night, preparing them for the next morning.

    All this move is highly____(benefit) to sunflowers. The team found that flowers kept away from the sun had leaves____were 10 percent smaller on average. According to Harmer, sunflowers which____ (face) with the sun receive more bees and other insects because they like warm flowers.