Which key morphological feature is used to classify organisms as mammals
a. the presence of fur
b. fertile offspring
c. mammary glands
d. two-legged upright posture

C. Mammary glands

Explanation:

The mammals have multiple different morphological features that distinguish them from the other animal groups, some are unique to them, some are unique as a combination. The morphological feature that is unique for the mammals and is most recognizable for them are the mammary glands. The mammary glands are actually the reason why this group of animals has the name it has. All three types of mammals, placentals, marsupials, and monotremes have these glands through which they feed their young.

the relative standard reduction potential of the half-cell in which reduction occurs; more positive than the other half-cell. reduction is a chemical process in which electrons are added to an atom or an ion; it always occurs accompanied by oxidation of the reducing agent.