Final answer:
A DDoS attack is when a hacker floods a network with too many requests, causing network traffic to be interrupted or stopped.
Step-by-step explanation:
The correct answer is A. DDoS attack. DDoS stands for Distributed Denial of Service. In a DDoS attack, the hacker overwhelms a network with a flood of requests from multiple sources, making it impossible for legitimate traffic to get through. This can cause the network to slow down or even crash.