stack nonterminal

例句：

1. 1. The boxes were stacked neatly on the shelves.
   箱子整齐地堆放在架子上。
2. 2. He stacked the books in a corner of the room.
   他把书堆在房间的角落里。
3. 3. The mountain was stacked with snow.
   山上堆满了雪。