<prompt> Retro pharyngeal space extends up to which of the following level?Base of skull to C6 vertebraBase of skull to bifurcation of tracheaBase of skull to the level of diaphragmBase of skull to cricoid cartilage  <response>: Refer: P. L. Dhingras Diseases of Ear, Nose and Throat Head and Neck Surgery, 6th edition, pg no: 265 