What is the purpose and potential applications of the "Expand Section" feature within the Visual Experience Composer (VEC)?

Which experience displays if a user qualifies for an activity that contains multiple experiences with multiple qualifying audiences?
For example, in the following illustration, a user from California using a Windows device qualifies for both Experience A (Windows audience) and Experience C (California audience).

Which factors determine the sample size for an A/B test? (Select two.)

What are key elements of an Experience Performance report in MVT? (Select two.)

An Adobe Target Business Practitioner has a standard A/B test that causes an inherent cost because it is spending traffic to measure performance of each experience individually to determine the winning experience.
Which solution is suggested to reduce the cost?