she was so angry an spoke so fast that none of us understand

what he said做一个名词成分 你可以替换成his words 然后代入
就是she was so angry and spoke so fast that none of us understand what his words meant

she was so angry an spoke so fast that none of us understand what (what he said) meant
Understand的宾语从句，STH mean what ，所以第一个填写what
而上所提到的STH即为这里的"what he said"
你可以这样理
she was so angry an spoke so fast that none of us understand what his word meant

可以这样用的
把这个句子写下来先
she was so angry and spoke so fast that none of us understand what what he said meant
what he said做一个名词成分 你可以替换成his words 然后代入
就是she was so angry and spoke so fast t...

第一个what 是连接understand, 就是明白甚麼的意思。 第二个what 是连接後面的he said meant. 不过如果你不懂的话，第二个也可以填that. 懂不？