What is this rule?

Sometimes its important to remove an RODC from yourforest or domain.
However, its important that you follow a simple rule whilst removing RODC’s. What is this rule?

A.
All RODC’s must be detached before removing a final writable domain controller

B.
All writable domain controllers must be removed before RODC’s can be detached

C.
Your forest must only consist of RODC’s if you want to remove them

D.
There are no rules for removing RODC’s

Explanation:
B & C are non sense
A is not about an RODC removal but about a writableDC and anyway if there is no more RWDC, RODC is non
sense…
either i don’t understand the goal of the question
or it’s simply the last answer (no rules)
==============
http://technet.microsoft.com/en-us/library/cc835490%28WS.10%29.aspx
RODC Removal and Reinstallation
This topic describes the different options and steps for removing a read-only domain controller (RODC)from a
domain. The following are the basic methods for removing Active Directory Domain Services (AD DS) froman
RODC:
You can remove AD DS and the RODC computer account in a single operation by using an account that is a
member of the Domain Admins or Enterprise Admins groups.
You can remove AD DS and the RODC computer account by using a two-stage operation, in which an
RODC delegated administrator removes AD DS from theRODC and then a member of Domain Admins or
Enterprise Admins removes the RODC computer account.
A delegated RODC administrator can remove AD DSfrom a computerto repair the software installation or
even replace the hardwareand then reinstall the RODC without intervention from a member of Domain
Admins or Enterprise Admins.
================
=> no particular requirement…
so far, the only requirements i know is about stolen or compromised RODC (we should reset all the passwords
that were stored in it but that’s it…