$\text { Identify any points at which the cycloid } x = \theta + \sin \theta , y = 1 - \cos \theta \text { is not smooth. }$

Multiple Choice

$\text { Identify any points at which the cycloid } x = \theta + \sin \theta , y = 1 - \cos \theta \text { is not smooth. }$

A) not smooth when $\theta = ( 2 n + 1 ) \pi$
B) smooth everywhere
C) not smooth when $\theta = ( 2 n ) \pi$
D) not smooth when $\theta = \frac { 1 } { 2 } ( 2 n + 1 ) \pi$
E) not smooth when $\theta = n \pi$