Answer
A is the symbol for parallel lines AB and XY.
Explanation
B shows that line segment AB and XY are parallel, because there are no arrows, and line segments do not extend forever.
C shows that ray AB and XY are parallel, because there is one arrow, and rays only extend on one point.
Only A shows that line AB and XY are parallel. Lines extend forever, the A shows that AB and XY are parallel, since there are arrows in both directions above AB and XY.
