A Block of Mass M Is Sliding Down a Rough $\theta$

Multiple Choice

A block of mass M is sliding down a rough inclined surface that makes an angle $\theta$ with respect to the horizontal. If the coefficient of static friction is $\mu$ _s and kinetic friction $\mu$ _k, then the acceleration of the block down the incline is equal to:

A) "g sin $\theta$ - $\mu$ _s g cos $\theta$ ."
B) " g cos $\theta$ - $\mu$ _k g cos $\theta$ "
C) " $\mu$ _s g cos $\theta$ -g sin $\theta$ "
D) "g sin $\theta$ - $\mu$ _k g cos $\theta$ "
E) "g sin $\theta$ - $\mu$ _s g cos $\theta$ - $\mu$ _k g cos $\theta$ "