Many trees____their green leaves in autumn.

lose

fall

fall好象不对，因为它是不及物名词。

fall

秋天的时候很多树叶都要掉叶子的。

shed

百分百保证！
1. Some trees shed their leaves in cold weather.
有些树在寒冷的天气里落叶。

2. Trees shed their leaves and flowers shed their petals.
到时候树就落叶、花就掉瓣.