pid t pid $=$ fork$()$: $//$ fork #$1$pid $=$ fork $()$; $//$ fork #$2$pid $=$ fork $()$ : $//$ fork #$3$pid $=$ fork$()$: $//$ fork #$4$If $($pid$==0)\{$fork $()$: $//$ fork #$5$fork$()$: $//$ fork #$6\}$fork $()$; $//$ fork #$7$a$)$ After executing fork#$4,$ how many processes are there in total? $[1$ Mark$]$b$)$ After executing fork#$6,$ how many processes are there in total? $[3$ Marks$]$C$)$ After executing fork#$7,$ how many processes are there in total? $[2$ Marks$]$