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Assume that a college student purchases only coffee and candy bars. What will the substitution effect associated with a decrease in the price of a candy bar result in$?$

a$.$ an increase in the consumption of coffee only

b$.$ a decrease in the consumption of coffee only

c$.$ an increase in the consumption of candy bars, and a decrease in the consumption of coffee

d$.$ a decrease in the consumption of candy bars, and an increase in the consumption of coffee

e$.$ None of the above.