Someone had played a trick on her, stretched a piece of string at the top of those steps.

有人对她搞恶作剧，在那些台阶的顶部拉了一根绳子。

《柯林斯英汉双解大词典》

I need a piece of string to parcel this up.

我需要一根绳子来把这东西捆起来。

youdao

Originally they were round pieces of metal with a hole in the center, so that a piece of string could keep them together.

最初它们是圆圆的金属片，中间有一个洞，这样一根绳子就可以把它们串在一起。

youdao

To keep himself awake as he flew east during the long night, Post tied a piece of string to one finger.

VOA: special.2009.03.18

Why not own a creature you can stroke and cuddle and tease with a piece of string?

BBC: Exotic pets: Why do Americans keep dangerous animals?

While he waits, a chain-smoking captain, Salih Yilmaz, busies himself with a plastic bottle and a piece of string, fishing for calamari to serve in his restaurant.

BBC: The perfect trip: Turkey

Four decades of arse parked inside a piece of string.

NEWYORKER: The Dog