Why is the nitrogen cycle considered a closed system?
a.
because nitrogen is fixed by bacteria and assimilated by plants
b.
because nitrogen neither enters nor leaves the system
c.
because nitrogen is converted into nitrates and ammonia
d.
because nitrogen is created by bacteria and destroyed by plants

B nitrogen stays in order so it can't change movement

does it have any answear choices.

explanation:

colorectal cancer may also develop from areas of abnormal cells in the lining of the colon or rectum. this area of abnormal cells is called dysplasia and is more commonly seen in people with certain inflammatory diseases of the bowel such as crohn's disease or ulcerative colitis.