You will be given a trivia clue, and the category it belongs to. You should answer with the best answer that belongs in the category and is described by the clue. For simplicity, answers should be in all lower cased letters.

Category: THE BODY WOMAN 
Clue: Shallower & wider than a man's to allow for childbirth, its bones are fused in a ring to give support
pelvis

Category: YOU GET AN "F" 
Clue: This type of cable contains threads of glass that transmit signals in the form of pulses of light
fiber optic

Category: ROCKY 
Clue: The greatest difference in hardness between 2 Mohs scale neighbors is between corundum (9) & this (10)

diamond