a pile of + n.作主语时，谓语动词的数应根据这个名词的数来决定。但在there be句型中，则出现了另一种情况。

A pile of papers (文件) were seen on the desk.

A pile of paper (纸) was found under the desk.

这一规则同样适用于piles of + n.，如：

Piles of old books are said to be on sale at the bookstore.

Piles of work has been done to solve the housing problem.

在There be句型中：

There was a pile of papers on the desk.

There are piles of old books in that room.