Select the option that is related to the third word in the same way as the second word is related to the first word.

Oology  :  Eggs  ::  Mycology  :  ?

Fungi 

The relationship between the first and second words seems to involve the study of a particular subject and its specific objects. In the first word, "Oology" is the study of "Eggs." Similarly, "Mycology" is the study of "Fungi."

So, the missing word is Fungi.