单项选择题

Penicillin was discovered by chance in 1928.

A．finally
B．accidentally
C．experimentally
D．opportunely
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单项选择题
Even with detailed knowledge about an area, geologists cannot easily locate stores of underground natural gas.
A．varieties
B．maps
C．supplies
D．shops
单项选择题
Before the Civil War, Frederick Douglass' editorials for the North Star urged respect for the rights of all people.
A．advocated
B．created
C．foresaw
D．granted
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