empty stack

例句：

1. 1. The empty stack of books on the desk is a clear sign that he has been absent for a long time.
   桌上那堆空书明显表明他已经很长时间没来了。
2. 2. The empty stack of books on the desk is a clear sign that he has been absent for a long time.
   桌上那堆空书明显表明他已经很长时间没来了。
3. 3. The empty stack of books on the desk is a clear sign that he has been absent for a long time.
   桌上那堆空书明显表明他已经很长时间没来了。