The situation is an example of negative reinforcement.
In the condition of negative reinforcement, a stimulus especially an unpleasant stimulus is removed due to a particular behavior of the person. In this case, the unpleasant behavior is the headache, and taking aspirin is a behavior of Nancy, which cut of the stimuli, that is pain relieving. In negative reinforcement a particular behavior is increased, in order to remove the unpleasant stimulus.
The distribuition of alleles changes due to random chance.
Answer:
Fossil fuels
explanation: Coal is one type of fossil fuel. This is a nonrenewable energy source whose extraction often damages the environment. Fossil fuels are made from decomposing plants and animals. These fuels are found in the Earth's crust and contain carbon and hydrogen, which can be burned for energy
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