TOPIC: How do you control scope if you have to add a new feature? What's the next step?

During Control Scope a new feature needs to be included into the scope updating the scope. What is next step?

A.) Issue a change request
B.) Gather detailed requirements on the new feature

The official correct answer is A because "the change request should be issued and approved before time and effort are expended on collecting detailed requirements on the new feature."

My question:

If I want to add details of the requirements to the change log it should need to be approved again because details my change the impact. Hmmm...
Or can I just add requirement details to the change log (includes the new requirment/feature) later after approval without any new approval required becaue it needed time to clarify the requirement details. I don't understand why B is not the next step and then A is done (B -> A)?
Which document do I update in control scope if I want to add a new requirement? Or is the update of the project document (change log) part of monitor and control procject work (project integration knowledge area)?

Thank's for an answer!

Source: Question ID: 70050