$($a$)$ Careful about the gradient model assumptions

$i=\frac{10}{\%}\frac{?}{\text{p}\text{e}\text{r}\text{i}\text{o}\text{d}}$

$($b$)$

$i=5\frac{\%}{p}$eriod

$>$

$($c$)$

netric gradient sel

$=g=10\frac{\%}{p}$eriod

$>$