单项选择题

The terrible pain during a crisis is caused by______.

A．the angular shape of the defective blood cells
B．the cutoff of oxygen supply in parts of the body
C．the cells stuck in the blood vessels
D．eating spoiled food

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热门试题

单项选择题

According to the passage, which is NOT TRUE of sickle-cell anemia

A．It is inherited.
B．It is not contagious.
C．It can be cured.
D．It occurs mostly in Africans.

单项选择题

In the Middle Ages, the copying work of books was mainly done by______.

A．monks
B．intellectuals
C．artists
D．merchants