$2.$ A cannonball is fired across a field. It rises into the air at first, then falls and strikes a target at the same elevation as the mouth of the cannon. How much work has been done on the cannonball by the force of gravity?

$($a$)$ none

$($b$)\backslash ($ m g $\backslash$cdot $\backslash )($the maximum height of the cannonball in flight$)$

$($c$)\backslash (2\backslash$mathrm$\{$mg$\}\backslash$cdot $\backslash )($the maximum height of the cannonball in flight$)$

$($d$)\backslash (-$m g $\backslash$cdot $\backslash )($the maximum height of the cannonball in flight$)$

$($e$)\backslash (-2$ m g $\backslash$cdot $\backslash )($the maximum height of the cannonball in flight$)$