The correct statements are For a given resource, a tag key must be unique and can map to only one value and Both AWS generated and user defined cost allocation tags must be activated separately before they appear in Cost Explorer or cost allocation reports.

Tags are simple key value pairs and for any given resource you can assign a tag key only once so the key holds a single value. This is why the first correct statement is true and why you cannot associate multiple values with the same key on the same resource.

The second correct statement refers to activation of cost allocation tags. Both AWS generated tags and user defined tags must be turned on in the Billing or Cost Allocation Tags settings before they are available in Cost Explorer and in cost allocation reports. Activating makes the tag keys visible for grouping and filtering in those cost tools.

Tags are required to run any cost or usage report is incorrect because you can generate cost and usage reports without tags. Tags help with grouping and filtering but they are not mandatory to produce reports.

Only user defined tags need activation to appear in Cost Explorer is incorrect because AWS generated tags also require activation before they show up in Cost Explorer or cost allocation reports.

For a resource, a tag key must be unique but can have multiple values is incorrect because a resource cannot have the same tag key assigned with more than one value.

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