A:did the quarrel come about
B:does the quarrel come about
C:the quarrel has come about
D:the quarrel had come about
古代世界各大洲、各地区和各民族的交往形式主要有两种。下列历史事件所体现的交往形式明显不同于其他三项的是( )
如图,直线AB、CD、EF相交于点O,则∠1+∠2+∠3的度数为( )