The correct answer is B.

Salesforce supports roll-up summary fields for summarizing related records, including scenarios involving Account and related Opportunity values. However, Salesforce documentation states that if Advanced Currency Management is enabled, currency roll-up summary fields are invalid when they are on Accounts and summarize Opportunity values.

Because the VP wants to aggregate Opportunity Amount values on Account, the app builder cannot create that roll-up summary field if Advanced Currency Management is enabled.

Why not others:

A is not the stated Salesforce limitation.

C is wrong because roll-up summary fields are available on Account in supported scenarios.

D is wrong because currency fields can be used in roll-up summaries generally; the issue is specifically Advanced Currency Management with Account-to-Opportunity currency rollups.