how long is a piece of string?
US /haʊ lɔŋ ɪz ə piːs əv strɪŋ/
UK /haʊ lɔŋ ɪz ə piːs əv strɪŋ/

1.
一根绳子有多长?, 无法给出确切答案的问题
used to say that it is impossible to give a precise answer to a question, because the answer depends on too many unknown factors
:
•
When asked how long the project would take, the manager replied, "How long is a piece of string?"
当被问及项目需要多长时间时,经理回答说:“一根绳子有多长?”
•
Trying to predict the exact outcome is like asking, "How long is a piece of string?" There are too many variables.
试图预测确切结果就像问:“一根绳子有多长?”变量太多了。