1 sentence for 空洞 (kōng​dòng — cavity; hollow)

1. 为什么臭氧空洞只发生在南极，而不是其他地方？

   wèi​shén​me chòu​yǎng​kōng​dòng zhǐ fā​shēng zài nán​jí, ér bù​shì qí​tā dì​fang?

   Why does the ozone hole only happen in Antarctica and not elsewhere?

   Source: CCMatrix