Your face becomes flush with
embarrassment, you begin to
sweat, and you can feel your
heart beating faster. What
system interactions brought
about this response?

i believe it would cause an increase of percipitation, though i could be wrong. so i would say b is the answer.

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

your answer is going to be physical weathering