体育场，为什么都是碗形？

Look at a big sports stadium. 你看看大体育场的样子。 It is usually shaped like a bowl. 它通常长得像一只大碗。 This shape puts seats close to the field. 这种形状，让座位离场地更近。 More people can watch at the same time. 同一时间，能坐更多观众。 The bowl also keeps cheers inside. 欢呼声，还能被拢在碗里。 The noise bounces and gets louder. 声音弹来弹去，越来越响。 That is why stadiums are built like bowls. 所以体育场，都盖成了碗形。