B) Ecosystem - which includes the living communities and nonliving factors in an environment
The main responsible for the delay among the atrial and
ventricular contractions is the action potential conduction velocity of the AV
node cells. If the atria and ventricles contract simultaneously, atria cannot
give any help in filling the ventricles, which is needed, especially in those
with stiff ventricles as in the elderly. Hence atria have to contract first and
then the ventricles.
Urine is stored in the Bladder before it leaves the body.
Going down A-D
Going across is 1-4
A 4
B 3
C 1
D 2
Hope this helps! Brainliest?
Have a great day :)
