When using Azure Translator REST API, required headers are: * Ocp-Apim-Subscription-Key # subscription key * Ocp-Apim-Subscription-Region # resource region (if using a multi-service Cognitive Services resource) * Content-Type # typically application/json or application/xml Other options: * Client trace ID is optional for debugging. * Resource ID, access control request, content language, content length are not required headers. The answer: B Reference: Azure Translator API reference