Explanation
The correct answer is A, B, and C. To inspect request processing of the APIs in APIM, you need to do the following three actions:
Enable the Allow tracing setting for the subscription used to inspect the API. This setting allows you to trace request processing in APIM using the test console, a REST client, or a client app. You can enable this setting in the portal by selecting Subscriptions and then selecting the subscription you want to use for debugging1.
Add the Ocp-Apim-Trace header value to the API call with a value set to true. This header triggers tracing when making requests to APIM using a REST client or a client app. You also need to add the Ocp-Apim-Subscription-Key header value to the key for a subscription that allows access to the API1.
Add the Ocp-Apim-Subscription-Key header value to the key for a subscription that allows access to the API. This header authenticates your request and grants you access to the API. You can find the key for your subscription in the portal by selecting Subscriptions and then selecting Show/hide keys1.
You do not need to create and configure a custom policy for tracing request processing. The trace policy is used to add a custom trace into the request tracing output, Application Insights telemetries, and/or resource logs2. It is not required for inspecting the APIs.