单项选择题

What is the main topic of the passage

A．The ways in which crows differ from other common birds.
B．The myths and legends about crows.
C．The characteristics that make crows difficult to study.
D．The existing methods for investigating crow behavior.

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单项选择题

According to the first paragraph, what evidence is there that crows have interested people for a long time

A．The large number of stories about crows.
B．The frequency with which crows are sighted.
C．The amount of research that has been conducted on crows.
D．The ease with which crows are identified.

单项选择题

According to the second paragraph, crows are poor subjects for field research for all the following reasons EXCEPT ______.

A．they can successfully avoid observers
B．they are hard to distinguish from one another
C．they can be quite aggressive
D．they are difficult to catch