Question: In an MBMS (Multimedia Broadcast/Multicast Service) scenario supporting scene description, how is the HTML5 presentation identified for clients?
Option 1: By the presence of an `appService` element in the USD with the attribute `appServiceDescriptionURI` set to point to the HTML5 document with the MIME type "text/html".
Option 2: Through a specific header in the FLUTE session indicating HTML5 content.
Option 3: By embedding the HTML5 document directly within the USD metadata without an external reference.
Option 4: Using a dedicated MBMS channel exclusively for scene descriptions.
Explanation: This is correct because, according to the specifications, the identification of the HTML5 presentation for MBMS clients relies on the presence of a specific `appService` element within the User Service Description (USD). This element must have its `appServiceDescriptionURI` attribute pointing to the HTML5 document, which is further identified by its "text/html" MIME type. This setup ensures that MBMS clients, which support scene description, can accurately locate and interpret the HTML5 content intended for presentation.