Which of these scenarios depicts a rational buyer? John walks into a grocery store and purchases monthly groceries without paying attention to the prices of groceries. Mary values a bag of salad at $2, but she buys the bag of salad even when the price is $4. Darwin buys a can of shoe polish at $4.50 when his marginal benefit from it is $3.75. Damien buys a sandwich for $5 when the marginal benefit of the sandwich to him is $7