《论语》云：“管仲相桓公，霸诸侯，一匡天下。”这则材料反映了什么历史事实？[ ]
A．晋文公称霸
B．齐桓公称霸
C．勾践称霸
D．楚庄王称霸
答案：B
The reporter has written ________ articles about air pollution hoping to call the attention of all people to
the problem.[ ]
A．a series of
B．a great deal of
C．a plenty of
D．a large amount of
有下列二叉树，对此二叉树前序遍历的结果为( )。
A．ACFXDBEYZ
B．ABEFXYZCD
C．ABCDEFXYZ
D．ABDYECFXZ
