Which option will be used with sort command to start sorting ofter the nth column of the (m+l)th field?

In the Unix sort command, the -k option is used to specify the key fields to be used for sorting. It allows you to define a custom sort field based on column position. The syntax for using this option is -k start[,end], where start and end are the positions of the starting and ending columns of the key field, respectively. The +m.n option specifies sorting starting after the nth column of the mth field.
Therefore, Option B is the correct choice.