D. He controlled variables by studying one or two traits at a time
Blood cells more then any other factor notice water doesn't have any cells in it and it flows freely and quickly.
Growth Hormone deficiency is a medical condition wherein the pituitary gland is not able to produce enough growth hormones also known as somatropins. This can be acquired either in childhood or adulthood. This condition is called hypopituitarism. Hope this is the answer that you are looking for.
The major organ of the circulatory system that causes blood to flow through the body by its pumping action is the heart.