Select the word-pair that best represents a similar relationship to the one expressed in the pair of words given below. (The words must be considered as meaningful English words and must NOT be related to each other based on the number of letters/number of consonants/vowels in the word)

Physiology : Human body

Petrology : Rocks

Physiology : Human body

The  logic followed here is :

THE STUDY OF HUMAN BODY IS PHYSIOLOGY

SIMILARLY

Petrology : Rocks

THE STUDY OF ROCKS  IS PETROLOGY