Some Deer Mice Are Physiologically Adapted to Live at High

Some deer mice are physiologically adapted to live at high altitudes because ____.

A) adults maintain fetal forms of hemoglobin
B) of mutations in hemoglobin that increase its oxygen-binding affinity
C) of mutations in myoglobin that increase its oxygen-binding affinity
D) of mutations that increase heart rates
E) of mutations that decrease heart rates