In Pavlovâs original experiments, a conditioned response that had been extinguished was seen again when the was delivered again. This reappearance of the conditioned response is known as .
a. unconditioned stimulus; spontaneous recovery
b. conditioned stimulus; reverse extinction
c. conditioned stimulus; spontaneous recovery
d. unconditioned stimulus; reverse extinction

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sulfur dioxide

explanation: acid rain is caused by a chemical reaction that begins when compounds like sulfur dioxide and nitrogen oxides are released into the air. these substances can rise very high into the atmosphere, where they mix and react with water, oxygen, and other chemicals to form more acidic pollutants, known as acid rain.

correct answer is a. and d.