Which of the following is an example of perfectly elastic demand?

• Susie always purchases three bagels on Friday because the bakery runs a special that day.
• Juan stopped purchasing peaches from his cousin's stall at the farmer's market when his cousin was the only farmer to raise prices.
• Danny got a tip that the price of downloads on iTunes was going to increase, so he purchased 20 additional songs today.
• The Smith family eats at the same pizza restaurant each week because they have the best sauce.