Which command will prevent the service ldap from starting on a Debian system in all runlevels,
forcing the removal of all symlinks in /etc/rcX.d? (Provide the command without any options or
parameters)

Answer: updaterc.d

Explanation:
From the man pages:
Update-rc.d – install and remove System-V style init script links
EXAMPLES
Insert links using the defaults: update-rc.d foobar defaults
Equivalent command using explicit argument sets: update-rc.d foobar start 20 2 3 4 5 . stop
20 0 1 6.
More typical command using explicit argument sets: update-rc.d foobar start 30 2 3 4 5 . stop
70 0 1 6.
Remove all links for a script (assuming foobar has been deleted already): update-rc.d foobar remove