$31.$ An activity has an early start $($ES$)$ of day $3,$ a late start $($LS$)$ of day $13,$ an early finish $($EF$)$ of day $9,$ and a late finish $($LF$)$ of day $19.$ The activity:

a$)$ Is not on the critical path.

b$)$ Has a lag.

c$)$ Is processing well.

d$)$ Is on the critical path.