Gills Serve Multiple Functions in Fish in Addition to Gas

Multiple Choice

Gills serve multiple functions in fish in addition to gas exchange.Given the large surface area of gills with lamellae,what is the most likely explanation for why crucian carp cover protruding lamellae in their gills when levels of oxygen are normal?

A) to prevent loss of heat to the surrounding water
B) to prevent loss of ions to the surrounding water
C) to prevent protein loss to the surrounding water
D) to prevent loss of oxygen to the surrounding water