which is an example of an internal stimulus?
a. a sudden change of air temperature
b. an artificial light that attracts insects
c. an increase in the amount of water available to a plant
d. a decrease in oxygen levels in the blood during exercise

A decrease in oxygen levels in the blood during exercise is an example of an internal stimulus. It is happening within the organism itself, it will be internal stimulus. But a sudden change of air temperature is not occuring within the body of organism.

It is the change outside so it is external. An artificial light that attracts insects and an increase in the amount of water available to plant. Both are happenings which occur outside the body hence both are external stimulus. Only a decrease in oxygen levels in the blood during exercise happens inside the body so it is only internal stimulus.

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-resources of geothermal energy range from the shallow ground to hot water and hot rock found a few miles beneath the earth's surface, and down even deeper to the extremely high temperatures of molten rock called magma

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-a geothermal heat pump system consists of a heat pump, an air delivery system (ductwork), and a heat exchanger-a system of pipes buried in the shallow ground near the building

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c. magnitude and direction