$4.$ If the value of user tool frame UT$[2]$ is $(0,0,0,0,0,0)$ in the robot system, then UT$[2]\_\_\_\_\_\_.$

$($a$)$ is not activated in the robot system

$($b$)$ cannot be used in recording robot point P$[$n$]$

$($c$)$ coincides with the robot$$s default TCP frame $($Def$-$TCP$)$ in the robot system

$($d$)$ coincides with the robot world frame R in the robot system