A distributed port scan operates by:

A distributed port scan operates by:

A.
Using denial-of-service software against a range of TCP ports

B.
Having multiple computers each scan a small number of ports, then correlating the results

C.
Blocking access to the targeted host by each of the distributed scanning clients

D.
Blocking access to the scanning clients by the targeted host

Explanation:
Think of dDoS (distributed Denial of Service) where you use a large number of computers to create simultaneous traffic against a victim in order to shut them down.