A large group of stars revolving around a center is known as a（）.

A group of stars which appear close together and form a striking configuration such as a person or animal is a（）.

A.cluster
B.shower
C.constellation
D.galaxy

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A first magnitude star is（）.

A.2.5 times as bright as a second magnitude star
B.3 times as bright as a second magnitude star
C.5 times as bright as a second magnitude star
D.10 times as bright as a second magnitude star

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