I think answer is A , B and D

A :
Omni-Channel routes work items from queues. By changing the record’s owner to a queue that has been configured for routing, you effectively trigger the routing process to test if the item gets pushed to an agent.

B :
Only users with Omni-Channel access (and assigned presence statuses) can receive routed items. Testing as such a user is essential.

C :
There’s no such “Debug Omni-Channel routing configuration” setting in Setup. You can monitor Omni-Channel routing with Supervisor or logs, but this option is made up.

D :
This lets you monitor real-time routing behavior — see agents’ statuses, routed work, and queues. It’s the right way to confirm items are being routed as expected.

E :
Not required. Opening a record doesn’t trigger routing ! assigning it to the queue does.