Question 352021
{{{drawing(300,300,-10,10,-10,10,circle(-7,0,0.3),circle(0,0,0.3),circle(7,0,0.3),locate(-7,-0.5,X),locate(0,-0.5,A),locate(7,-0.5,B),line(-20,0,20,0),line(8,0,7.5,0.5),line(8,0,7.5,-0.5),
circle(0,-4,0.3),circle(7,-4,0.3),line(0,-4,20,-4),line(8,-4,7.5,-4.5),line(8,-4,7.5,-3.5),locate(0,-4.5,A),locate(7,-4.5,B))}}}
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I think it's just a wording issue.
The line AB could also be thought of as line XB or XA, it's the same line(since X,A,and B are collinear), it's just how you name it.
However, ray AB starts at point A and goes in direction from A to B. 
I think this illustration easily shows that ray AB is a subset of line AB (or XB). 
Now put it into words.