For any circle, let Quantity P be the ratio of the length of an intercepted arc to the radius, and Quantity Q be the measure (in radians) of the central angle subtending that arc. Which of the following correctly compares P and Q?
a) P is always less than Q.
b) P is exactly half of Q for every arc.
c) P equals Q for all arcs.
d) P equals Q only when the radius is 1; otherwise they differ.