Answer:
The return of blood to the heart is assisted by the action of the skeletal- muscle pump. As muscles move, they squeeze the veins running through them. Veins contain a series of one-way valves, and they are squeezed, blood is pushed through the valves, which then close to prevent backflow.
Answer:
True
Explanation:
According to the law of conservation of mass, mass can not be created nor destroyed.
The implication of this is that the total mass on both sides of the reaction equation must be the same.
Thus, the number of atoms of each element on both sides of the reaction arrow must be the same.
(1) normally harmless cat antigens stimulated
<span>the immune system</span>
