The correct option is (b) Ogg Theora Vorbis
To elaborate: Ogg format is supported in mobile, desktop, chrome, safari, opera. WebM is preferable over Ogg Theora Vorbis due to the better ratio of compression and quality and most of the browsers support WebM. Ogg format can be used to support old browsers. The MIME type of Ogg file that has audio is audio/ogg.