517. The students discussed their list of the world's greatest inventions. Then they voted for their favorite. As Ms. Brown expected, smart phones won. She said, "Now, let's discuss inventions with no computer chips or moving parts. And no edible parts, either. Everything must be simple and portable. Name your favorites. I'll write them on the board. Later, we'll discuss them and vote for our favorite. Johnny, let's start with you." Johnny said, "Surfboards!" Ms. Brown said, "They're a little too big for our list." Johnny said, "Skateboards!" Ms. Brown said, "No moving parts, please. I'll get back to you, Johnny. Sara?" Sara said, "Spoons!" Ms. Brown wrote "spoons" on the board. She called on each student. Students named baseball caps, flip‐flops, and mirrors, among other things. Finally, she called on Johnny again. He said, "I've got the winner. It fits in your hand, and there's no moving parts—toilet paper!" 3.4