The correct choice is US East (N. Virginia) - us-east-1. CloudWatch billing metrics are global and are stored and retrieved from US East (N. Virginia) - us-east-1 for the account regardless of where workloads run.

Billing and the EstimatedCharges metric are published to the CloudWatch endpoint in us-east-1 and you must query that Region to view company wide estimated charges. Centralizing the data in one Region allows a single dashboard to represent costs from all Regions for the account.

US West (N. California) - us-west-1 is incorrect because AWS does not store billing metrics there and you will not find the EstimatedCharges metric in that Region.

The Region hosting the provisioned resources is incorrect because billing metrics are not tied to where workloads run and CloudWatch publishes billing data centrally instead.

The Region where the AWS account was initially set up is incorrect because the account creation Region does not determine where billing metrics reside and AWS uses the global endpoint in us-east-1.

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