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【单选题】
花粉囊壁的哪一个细胞层的变化有助于花粉囊开裂和花粉散出？A.
药室内壁（纤维层）
B.
表皮
C.
绒毡层
D.
中层
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反馈参考答案：
举一反三
【单选题】听力原文：Migratory birds use several ways to help them navigate. While traveling on a clear night they use the stars as guides. On cloudy nights, they may be using the earth's magnetic field or the wind t...
A.
正确
B.
错误
【单选题】During daylight hours, birds ______.
A.
fly aimlessly
B.
rely on landmarks
C.
use sun for guidance
D.
are more likely to get lost
【单选题】Most birds find it safe to sleep in the trees, but they have eggs or young chicks, they don't use a nest. [ ]
A.
why
B.
how
C.
unless
D.
where
【单选题】—How do people do bird-watching? —Sometimes they______the birds quietly, sometimes they use telescopes.
A.
catch
B.
cast
C.
approach
D.
Shoot
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