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A. they make us think about our universe
B. they were used to represent some other phenomena
C. they are more precise than theories
D. they indicate further direction and help us make predictions

A. Women enjoy using umbrellas with various kinds of colors nowadays.
B. The inventor of the umbrella is unknown.
C. Once ordinary people had no right to use umbrella.
D. Umbrellas were popular and cheap in ancient times.