Which statement best describes ecosystems? A. they can never change once they are established
B. they constantly change in different ways over time
C. ecosystems always revert back to their original state
D. each ecosystem can exist for only a specific lenght of time

b. they constantly change in different ways over time.

Explanation:

different factors affect ecosystems which end up changing them in different ways

what are the options

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)]