为什么Playing computer games sounds relaxing中的sound要加s?

为什么Playing computer games sounds relaxing中的sound要加s? Playing computer games.中的playing为什么要加ing? computer,playing,interesting,sounds,games(.) It's sounds great,为什么sound要加s? That sounds good.这里的sound为什么要加s? That sounds good的sound为什么要加s?直接sound不好了 That sounds good中的sounds为什么要加s my english teacher's voice sounds中sound为什么要加s That sounds boring.为什么sound加s啦 the song sounds very nice中,sound为什么加s? Don't spend your free time playing computer games.中play为什么要加 为什么 We like computer games 要加"s",而 Let's play computer game