In the Johannine literature (Gospel of John and the Johannine epistles), what is the significance of the term 'Paraclete' (Comforter/Advocate)?

A A reference to John the Baptist as the forerunner of Jesus. B A title exclusively for Jesus Christ in his role as mediator. C A designation for the Holy Spirit, sent by Jesus to continue his work and presence among believers. D A term used to describe the angels who minister to believers.