The children sat mute in the corner of the room.
这里sit是一个不及物动词，而mute(a.沉默的)是一个主语的补足语，它说明了主语(children)的状态。mute和sit两个单词本身在句子中的位置没有必然联系，也因此sit并不是系动词。它的位置可以变动如下：
The children sat in the corner of the room, mute.
Mute, the children sat in the corner of the room.
形容词作主语补足语形成一个无动词分句插入在句子中，它的位置一般在实意动词后、句子开头和末尾，说明主语的状态。例如：
In a cold winter evening, all money stolen, thousands of meters far from home, they sat in a corner of the city, cold and hungry, trembling and praying for someone to rescue them.
He made it home, exsausted.
Nervous, he entered the police station.