.ad [c]Adjust output lines according to format c.  Fill mode must
be on (see .fi).
With no argument, return to previous adjustment.
The current adjustment mode is
stored in register .j, with the following values: 0=l, 1=b, 3=c,
5=r (see .na).
Lines are justified.
Lines are justified.
Lines are centered.
Lines are flush left.
Lines are flush right.