Which principal ray in a standard ray diagram for a thin lens travels in a straight line through the lens without bending?
a) A ray that passes through the near focal point and then continues straight through the lens.
b) A ray that is initially parallel to the principal axis and therefore continues straight through the lens without bending.
c) A ray that passes through the center of the lens and continues in the same direction.
d) A ray that strikes the lens halfway between the axis and the edge, where the curvature is minimal, so it keeps the same direction.