Callous is another way to say it
A. It has mass.
Air is matter, and can't be seen thus not all matter can be seen.
Any liquid or gaseous is matter (water, air, etc.)
Since it can be liquid or gaseous it doesn't have to maintain it's shape and size to be matter.
The free nerve endings
can detect pain, temperature, itch and hair movement. Merkel's disks can detect pressure, position and static touch features. Pacinian corpuscles are sensitive to vibration while Meissner's corpuscles are sensitive to light and touch.
The correct answer to this question is this one: a.) bottleneck effect. Increased poaching nearly led to the extinction of the American bison. The kind of effect that does this example represent is called the bottleneck effect. Hope this helps answer your question.
