A new participant is added to the top of the stack if it is not already on the way - in this case, the stack is cut off to that one.
如果还没有开始一个新的参与者，则它将被放入堆栈的顶部—在本例中，对新参与者关闭了堆栈。
2
In the faint light of the attic, an old man, tall and stooped, bent his great frame and made his way to a stack of boxes that sat near one of the little half-windows.