everyone：单数形式,复数概念.例：
Everyone is happy in our group.
nobody：单数形式,“否定”概念.例：
Nobody is happy in our group.
someone：单数形式,“不定指”概念（不特指某一人）.例：
Someone is happy in our group.
anyone：单数形式,泛指概念（可以是任何人）.例：
Anyone can do the job in our group.
用于疑问句中：
Can anyone do the job?Anyone knows?