Which of the following would be MOST effective in reducing the impact of a distributed...

The answer to the question is B. Spread a site across multiple ISPs. This is because spreading a site across multiple Internet service providers (ISPs) can help to reduce the impact of a distributed denial of service (DDoS) attack by increasing the bandwidth and redundancy of the site, and making it harder for the attacker to target and overwhelm a single point of failure. Spreading a site across multiple ISPs can also help to distribute the traffic load and balance the performance of the site, and to mitigate the effects of regional or network-specific outages or disruptions. Spreading a site across multiple ISPs can be done by using various techniques, such as anycast routing, content delivery networks (CDNs), or cloud-based services12.

Spreading a site across multiple ISPs can help to reduce the impact of a DDoS attack by increasing the bandwidth and redundancy of the site, and making it harder for the attacker to target and overwhelm a single point of failure. (From CISM Manual or related resources)

References = CISM Review Manual 15th Edition, Chapter 4, Section 4.2.1, page 2091; DDoS Attacks—A Cyberthreat and Possible Solutions2