题目内容：

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 1. how and why young sunflowers move.

Older sunflowers always face east. However, as it 2.(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 3. (explain) in a recent paper published in the journal Science on Aug. 5.

4. (depend) on the time of day, certain growth genes seem to work to different degrees on different 5. (side) of young sunflowers’ stems（茎）. The east side of their stems grows faster during 6. day, causing the stems to 7. (gradual) bend from east to west. The west side grows faster at night, preparing them for the next morning.

All this move is highly 8. (benefit) to sunflowers. The team found that flowers kept away from the sun had leaves 9. were 10 percent smaller on average. According to Harmer, sunflowers which 10. (face) with the sun receive more bees and other insects because they like warm flowers.