Describe the evolution of a pulsar over time, in particular how the rotation and pulse signal changes over time. (Select all that apply.) 

a. The pulsar loses energy, which decreases its pulse signal. 

b. The pulsar loses energy, which decreases its rate of rotation. 

c. The pulsar collapses in on itself, which increases its rate of rotation. 

d. The pulsar collapses in on itself, which increases its pulse signal.