单项选择题
Barack Obama，（）African America，was elected as（）56th President of the United states.
A./；theB./；/C.an ；theD.an ；/
单项选择题 It is not （）to discuss the questions again and again.
单项选择题 Their working conditions（）the same （）before.
单项选择题 It is said that the weather will（）hot for another three or four days.
