But for real trees, it’s harder to uproot. Because they’re literally rooted into the ground, they are unable to leave and go (26)_____. When a tree first starts growing in a certain area, it’s likely that the (27)_____ envelope—the temperature, humidity, rainfall patterns and so on—suits it. Otherwise, it would be unable to grow from a seedling. But as it (28)_____, these conditions may change and the area around it may no longer be suitable for its (29)_____. When that happens, many trees like walnuts, oaks and pines, rely (30)_____ on so-called “scatter hoarders”, such as birds, to move their seeds to new localities. Many birds like to store food for the winter, which they (31)_____ retrieve. When the birds forget to retrieve their food—and they do sometimes—a seedling has a chance to grow. The bird Clark’s nutcracker, for example, hides up to 100,000 seeds per year, up to 30 kilometers away from the seed source, and has a very close symbiotic (共生的) relationship with several pine species, most (32)_____ the white bark pine. As trees outgrow their ideal (33)_____ in the face of climate change, these flying ecosystem engineers could be a big help in (34)_____ trees. It’s a solution for us—getting birds to do the work is cheap and effective—and it could give (35)_____ oaks and pines the option to truly “make like a tree and leave”.

* 本题备选项需点击原文空格处获取，在列表上点选即可。    The tree people in the Lord of the Rings—the Ents—can get around by walking. But for real trees, it’s harder to uproot. Because they’re literally rooted into the ground, they are unable to leave and go (26)_____.    When a tree first starts growing in a certain area, it’s likely that the (27)_____ envelope—the temperature, humidity, rainfall patterns and so on—suits it. Otherwise, it would be unable to grow from a seedling. But as it (28)_____, these conditions may change and the area around it may no longer be suitable for its (29)_____.    When that happens, many trees like walnuts, oaks and pines, rely (30)_____ on so-called “scatter hoarders”, such as birds, to move their seeds to new localities. Many birds like to store food for the winter, which they (31)_____  retrieve. When the birds forget to retrieve their food—and they do sometimes—a seedling has a chance to grow. The bird Clark’s nutcracker, for example, hides up to 100,000 seeds per year, up to 30 kilometers away from the seed source, and has a very close symbiotic (共生的) relationship with several pine species, most (32)_____ the white bark pine.    As trees outgrow their ideal (33)_____ in the face of climate change, these flying ecosystem engineers could be a big help in (34)_____ trees. It’s a solution for us—getting birds to do the work is cheap and effective—and it could give (35)_____ oaks and pines the option to truly “make like a tree and leave”.