Whenever an object is moving at a constant rate, the value(s) that equal zero is (are): a) Speed
b) Acceleration
c) Velocity
d) All of the above

Whenever an object is moving at a constant rate . . .

a).  its speed is that constant rate.

b).  Its acceleration MAY BE zero, if it's also moving in a straight line.

c).  Its velocity is that constant rate if it's moving in a straight line.  Otherwise, its velocity could have many different values, depending on the path it's following.  

the motion of a pendulum is a classic example of mechanical energy conservation. a pendulum consists of a mass (known as a bob ) attached by a string to a pivot point. as the pendulum moves it sweeps out a circular arc, moving back and forth in a periodic fashion.