The correct answer is Region, pricing tier and hourly billing.

Specifically, Region, pricing tier and hourly billing is correct because Azure Cache for Redis pricing varies by geographic region and by the SKU or tier you choose, and the service is metered on a time basis so costs are calculated hourly for provisioned instances.

Charges per operation or per transaction is incorrect because Azure Cache for Redis is not billed per individual cache operation or transaction. The service is provisioned as an instance and pricing is based on the instance tier and time rather than per request.

Region, allocated memory and pricing tier is incorrect because although memory capacity is related to the chosen tier, billing is expressed by the tier and by time. This option omits the important hourly billing dimension that determines how charges accumulate.

Region and pricing tier is incorrect because it leaves out the billing period. Region and tier affect price levels but the actual charges are applied on an hourly basis for the provisioned instance.

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