1) An object moves along a line so that its position at time t is s(t) = t^4 - 6t^3 - 2t - 1. At what time t is the acceleration of the object zero?

A. at 3 only

B. at 0 and 3 only

C. at 0 only

D. at 1 only

2) If f(x) = e^x (sin x + cos x), then f'(x) =

A. 2e^x (cos x + sin x)

B. e^x cos x

C. e^x (cos^2x - sin^2x)

D. 2e^x cos x