Final answer:
The correct approach for requesting JSON from an API is to use the Accept header with the value 'application/json'. This informs the server that you expect a JSON response. The Content-Type header is used for sending data, not requesting it.
Step-by-step explanation:
The best approach for requesting JSON instead of XML from an API is D. Use the Accept header. When making an HTTP request to an API, the Accept header is used to tell the server the type of content you expect in response. By setting this header to 'application/json', you indicate that you prefer to receive a JSON formatted response. Some APIs also support appending '.json' to the end of the URL as an alternative way to request JSON, but this practice is not standardized and may not work for all APIs.
However, the Content-Type header, which is used for specifying the type of data you're sending to the server, should not be confused with the Accept header. Contrary to option B, APIs can indeed use XML, but the trend has shifted towards JSON because it's typically lighter and easier to work with in web applications.