单项选择题

The hydra is a kind of______.

A．flatworm
B．coelenterate
C．sea anemone
D．nerve cell
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单项选择题
It can be inferred from the passage that insects do not have______.
A．brains
B．backbones
C．nerve cells
D．reflexes
单项选择题
With what topic is the passage mainly concerned
A．The sensory organs of invertebrates.
B．The anatomy of tiny organisms.
C．The origin of the brain and central nervous system.
D．The importance of vision for fish and advanced mammals.
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