Steve went to his favorite hamburger restaurant with $3, expecting to buy a $2 hamburger and a $1 soda. when he arrived he discovered that hamburgers were on sale for $1, so steve bought two hamburgers and a soda. steve's response to the decrease in the price of hamburgers is best explained by:
a. the substitution effect.
b. the income effect.
c. the price effect.
d. a rightward shift in the demand curve for hamburgers.