Preparing all the needed items is important to successful project.请问为何用is.

Preparing all the needed items is important to successful project.请问为何用is.
Preparing all the needed items is important to successful project.请问为何用is.

Preparing all the needed items is important to successful project.请问为何用is.
【Preparing all the needed items】主语【 is important to 】谓语【successful project.】宾语
从句子成分分析知道,Preparing all the needed items 是-ving形式短语,即动名词短语,作主语.按照英语语法,不定式、动名词、从句作主语,表示单一内容或指代单一对象时,谓语动词用单数.因此,后面用了is.
【 Preparing动名词】+【 all the needed items】宾语（或状语）=动名词短语
句意：准备所有这些物品是该项目成功的关键.

主语是preparing,所以用is。

主语是preparing,"all the needed items"是修饰主语的定语。

这句用is是因为主语是preparing而不是items
本句的意思是，对所需元素的准备，对于一个成功的项目来说十分重要。

动名词短语做主语,谓语用单数