Answer:
Closed the first one
Explanation:
In amphibians, reptiles, birds, and mammals, blood flow is directed in two circuits: one through the lungs and back to the heart, which is called pulmonary circulation, and the other throughout the rest of the body and its organs including the brain (systemic circulation).
most mammals, have closed cardiovascular systems. The two main circulation pathways in invertebrates are the single and double circulation pathways.
To avoid any injuries or emergencies <span />
Answer:
Rocks or lava
Explanation:
In 1° succession there is no soil.. And the process of soil formation take very long time.
In 1° succession rocks or lava is present and lichens, soil erosion, wheathring of rocks helps in soil formation.
