$2\%$ Which one of the following is correct?

$($a$).$ Android cannot provide the same level of protection as UNIX, because it is not able to separate users.

$($b$),$ root user can modify mandatory access control $($MAC$).$

$($c$).$ Role$-$based access control $($RBAC$)$ increases the security risk associated with superusers.

$($d$).$ Apple's systems employ capability$-$based protection in the form of entitlements.