单项选择题

After two years he received the certificate of the college for ______ in chemistry.

A．proficiency
B．diversion
C．immersion
D．involvement
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单项选择题
Slavery was ______ in the U.S. in the 19th century.
A．retailed
B．canceled
C．abolished
D．stroked
单项选择题
Ladies and gentlemen should always act with great ______.
A．impulse
B．dignity
C．temperament
D．symmetry
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