Which is an example of someone using a simple machine to do work ?

Question

$\begin{array}{1 1} (a)\; \text{a boy runs across a football field } \\ (b)\; \text{a banker counts money } \\ (c)\; \text{lady pushes a stroller up the building } \\ (d)\; \text{a old man walking with a walking stick} \end{array}$