Solve the Problem $\mathrm { v } = \frac { \mathrm { k } } { \mathrm { s } } ( \mathrm { k }$

Solve the problem.
-Suppose that the velocity of a falling body is $\mathrm { v } = \frac { \mathrm { k } } { \mathrm { s } } ( \mathrm { k }$ a constant) at the instant the body has fallen s meters from its starting point. Find the body's acceleration as a function of s.

A) $a = - \frac { k ^ { 2 } } { s ^ { 3 } }$
B) $a = - \frac { 1 } { s ^ { 2 } }$
C) $a = \frac { k ^ { 2 } } { s ^ { 3 } }$
D) $a = - \frac { k } { s ^ { 2 } }$