“封闭的”用英语怎么说

窗户通常是封闭的。Windows are usually sealed off.他们接触的事不多，从这一方面来说这是个封闭的社团。It is a closed society in the sense that they've not been exposed to many things.宇宙究竟是开放的,还是封闭的?Is the universe open or closed?...