What is the format of structured notification messages sent by Amazon SNS?

A.
An XML object containing MessageId, UnsubscribeURL, Subject, Message and other values

B.
An JSON object containing MessageId, DuplicateFlag, Message and other values

C.
An XML object containing MessageId, DuplicateFlag, Message and other values

D.
An JSON object containing MessageId, unsubscribeURL, Subject, Message and other values