"detection" by checking for possible cycles or knots.
Answer:
Nonexclusive forwarding
Explanation:
In Nonexclusive forwarding, DNS forwarding is setup so that if the DNS server receiving the forwarded request cannot resolve the name, then the server that originally forwarded the request makes an attempt to resolves it. If that fails, the server sends a request to its designated forwarder.
The answer to this problem is A, one-to-one.
There's another question I found like this which 2 people answered with either C2 or B3. (B3 was rated with 5 stars but I don't know if that was the user them-self)