A.) Veins in the pulmonary circuit carry oxygen-rich blood
red blood cells are used to circulate oxygen through out the body, thus it is true.
The carbon cycle maintains the balance between the organic remains and carbon dioxide. In this cycle the the incorporation of carbon dioxide inside the plants by photosynthesis occurs and it is returned to the atmosphere by the process of respiration as well as the decaying dead organisms.
The answer would most likely be C
When SA Node triggers Atria goes into Systole !! and when the signal reaches to AV node and from there it goes to Bundle of His making Ventricle to systole or constrict !!
So your answer is Systole !!
