Which tool can be used during the "Plan" phase to build audience strategies leveraging first-party data and shopping signals?

Amazon Marketing Cloud (AMC) is the correct answer because it is a secure, privacy-safe clean room solution that allows advertisers to perform advanced analytics on their Amazon Ads campaigns and other datasets. During the "Plan" phase, AMC can be used to leverage first-party data and Amazon shopping signals to build sophisticated audience strategies, identify new customer segments, and understand customer journeys. Report Builder and Reporting API are tools primarily used for generating and accessing performance reports, not for advanced audience strategy development using combined datasets.