Let `vec(v)` and `vec(a)` denote the velocity and acceleration respectively of a body in one-dimensional motion.
A. `|vec(v)|` must decrease when `vec(a) lt 0`
B. Speed must increase when `vec(a) gt 0`
C. Speed will increase when both `vec(v)` and `vec(a)` are `lt 0`
D. Speed will decrease when `vec(v) lt 0` and `vec(a) gt 0`
