<prompt> Which structure marked below would be responsible for spreading infection into anterior pa of the middle nasal meatus through the frontonasal duct?ABCE  <response>: The frontal sinus drains into the anterior pa of the middle nasal meatus frontonasal duct or infundibulum. A.- Cerebrospinal fluid CSF is formed by vascular choroid plexus in the ventricles in the brain; the letter A indicates the lateral ventricle. C.- The maxillary sinus lies lateral to the lateral wall of the nasal cavity and inferior to the floor of the orbit. B.- Mastoid air cells communicate with the middle ear cavity through the antrum and aditus. D.- The ethmoid sinus has numerous small cavities and lies between the orbit and the nasal cavity. 