Consider the following code snippet:

vector num$(3)$;

num $[0]=1$

num $[1]=2$

num $[2]=3$

num.$po{p}_b$ack$()$;

Which element or elements of the vector are removed by the pop$\_$back$()$ in the given code snippet? $q,$

The element with index number $0$

The element with index number $1$

The element with index number $2$

All the elements