Concept:The six authentic books of Hadith are jointly known as Sihahus-sittah.Explanation:The term "Sihahus-sittah" means "the six authentic ones."These six books contain the sound sayings and actions of Prophet Muhammad (SAW).They are the major Hadith collections accepted by Sunni Muslims.The correct option is therefore C, Sihahus-sittah.Answer:C. Sihahus-sittah