All of them or ....
what question?
Explanation:
excretory system is present in human body which discharge out the waste material time to time. basically when a cell in a body breaks down they produce various waste material like carbohydrates eliminates carbon dioxide while digestive system eliminates through feces. any malfunctioning can cause serious problem like constipitation kidney failure and kidney stones
B Gradually develops stiff outer cell wall for protection is the answer
Answer:
C. the AV node will usually become the pacemaker for the heart