a,b,c,d在一条直线上,则有几条线段?几条射线?

问题描述:

a,b,c,d在一条直线上,则有几条线段?几条射线?
(请写出原因)
几条射线?各是哪几条?

1.a____________b___________________c______________d________2.a_________________b________________c___________________________d3._____a______________b________________c____________________d_______4._____...