Which of the following could be said about ecological footprints?
a. ecological footprints don't take into account resources needed to absorb and manage wastes.
b. exact ecological footprints are often difficult to calculate, but estimates can be useful in comparing populations.
c. the average ecological footprints for various countries are nearly identical.
d. ecological footprints can't be used to determine carrying capacity.

there are so many examples for that in different areas, like biology experiment carried out in our lab recently.

here's one link:

answer : haversian

[explanation: -(compact bone is organized as parallel columns, known as haversian systems, which run lengthwise down the axis of long bones. these columns are composed of lamellae, concentric rings of bone, surrounding a central channel, or haversian canal, that contains the nerves, blood vessels, and lymphatic system of the bone)]