close
当动词时是 “关、闭上”的意思
例如：close the door; close your eyes ...
当形容词则为“亲近、亲密”的意思
例如：Tom and I were really close when we were in high school.
closed
主要就是形容 xx 是“关着的、封闭的、不在营业中”
例如：The library is closed on Sunday.
closely
主要是副词功能,用来修饰动词时表达“很接近地、紧密地、密切地”
例如：The crowd closely watch the players' every move as the clock winds down.
三个词各有各的基本功能,必须根据语境试着去理解揣摩.上面提供的只是在常态下的用法.