A Block Is at Rest on a Frictionless Horizontal Plane $\theta$

Multiple Choice

A block is at rest on a frictionless horizontal plane. As one end of the plane is slowly raised, the block eventually "breaks loose" when the plane makes an angle, $\theta$ , with the horizontal. At this moment the coefficient of static friction is

A) sin $\theta$
B) cos $\theta$
C) tan $\theta$
D) cot $\theta$