Which of the following BEST describes varicose veins? A. Veins cannot prevent the backflow of blood.
B. Veins lose the ability to transport blood to the heart.
C. Veins become used for transporting blood to and from the heart.
D. Veins become less efficient at transferring waste to the blood.

stimulus is a change in the environment that causes an organism to react. the response is the reaction to the stimulus. some examples of stimuli for zebras are drought, to many predators, and bad feeding grounds such as dead grass or plants. zebras respond to stimuli just like all other living organisms