I think both A and D are correct, however the answer sought is 'A', as it is specifically worded as, Which "opportunity" helps ? If you refer to "opportunities" in Domain 10 "Elasticity" is listed as an Opportunity Heading, including the justification.

Definitely D, even some choices seems to be selected from the text some quated below (reversing, for example, the "Increased use of Micro services" to confuse)

Segregation by default can indeed help reduce common application security issues. By implementing segregation by default, applications and systems are designed to separate different components, resources, or user access by default. This approach helps prevent unauthorized access, limit the impact of security breaches, and reduce the attack surface.

The opportunity that helps reduce common application security issues is: D. Segregation by default Segregation by default refers to the practice of isolating different components and resources within an application or system by default. By implementing proper segregation measures, such as network segmentation and access controls, organizations can reduce the risk of unauthorized access and limit the potential impact of security breaches. This approach helps prevent lateral movement and contains the impact of any compromised component or system. By enforcing segregation as a default principle, organizations can enhance application security and minimize the potential for common security issues.

It's Elasticity. As it enables greater use of immutability

10.1.5 Some of these have nothing directly to do with security, but the following trends offer opportunities to reduce common security issues: • Segregation by default

Secuirty Guidance 10.1.5: Sgregation by default, inmmutable infra, increased use of micro-services, paas and serverless arch.

From de guidance. Elasticity enables greater use of immutable infrastructure. When using elasticity tools like auto-scale groups each production system is launched dynamically, based on a baseline image, and may be automatically deprovisioned without human interaction.

Correct Answer is Option D: Segregation By Default Reference: Segregation by default: Applications can easily be run in their own isolated cloud environments. Depending on the provider, this could be a separate virtual network or account/sub-account.

Elastic infrastructure is Immutable infrastructure.

Following trends offer opportunities to reduce common security issues: Segregation by default, Immutable infrastructure, Increased use of micro-services, PaaS and "serverless" architecture.