that the dog was the first animal to be domesticated is generally agreed upon by

题目

that the dog was the first animal to be domesticated is generally agreed upon by
authorities in the field 为什么是dog 前面要填that the 而不是the

答案

That 引导主语从句.
主语：That the dog was the first animal to be domesticated
谓语：is generally agreed upon by authorities in the field

我们完全可用问题中的句子作一篇文章的第一句,然后接着写下去,根本不必有任何“前文”.