a piece of paper后的谓语动词用单数还是复数

a piece of+单数
pieces of+复数
There is a piece of paper.

There are pieces of paper.

用单数

单数
a piece of修饰不可数名词
paper是不可数名词
因此需要用单数
There is a piece of paper on the desk.桌子上有一张纸。

用单数。此类短语的谓语动词用单数还是复数，主要看量词（这里为piece）的单复数
eg. There is a piece of paper.
there are several pieces of paper.