Barrack Obama President of the United States since 2010.
A. became a
B. has bee a
C. has turned
D. has been
网友回答
A. became a
B. has bee a
C. has turned
(答案→)D. has been
解析：Barrack Obama自从2010年一直是美国的总统。和since 2010连用，用现在完成时，而且因为是一段时间，所以不能和短暂动词bee连用，所以选D。