Aunique characteristic of mammals is that they

a.) have hair
b.) have a four-chambered heart
c.) have both aquatic and terrestrial species

The correct answer for the blank is- A) Have hairs.

As per the University of Michigan, there are primarily three characteristics/ features that are unique to mammals. These are as follows-

1) Presence of hairs on body.

2) Presence of mammary glands ( primarily used of feeding the neonates).

3) Presence of three bones in the middle ear ( that is Malleus, incus, and stapes).

The most significant function of hairs in mammals is that they provide insulation against cold by conserving heat of body. In certain nocturnal animals ( which are active during night time), they serve as sensory organs.

Thus, option A) is the right answer.

i would have to say autosomal

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