How Do the Ears of Mammals Differ from Those of Birds

How do the ears of mammals differ from those of birds and reptiles?

A) Mammalian ears have three small bones to transmit vibrations to the cochlea,while the other species have only one bone.
B) Birds and reptile ears have the pinna and mammalian ears don't.
C) The inner ear in mammals have liquid filled in it whereas inner ears of reptiles and birds do not have liquid filled in their inner ear.
D) Reptiles and birds have more hair cells than mammals.