I am reviewing for AP Calc test and I need some help b/c i don't remember how to quite do this problem.

the position of a particle moving along a straight line is given by

$\displaystyle s=t^3-6t^2+12t-8$

a. the minimum value of the speed is:

(A) 1 (B) 2 (C) 3 (D) 0 (E) none of these

b. the speed of the particle is decreasing for:

(A) t>2 (B) t<3 (C) all t (D) t<1 or t>2 (E) none of these