This document provides information about identifying the subject of a sentence using "x-words". It defines x-words as 20 common words in English that sentences are built around, including forms of "to be", "to have", and "to do". It explains that the subject of a sentence can be identified by finding the x-word, making it the first word to form a yes/no question, and noting what words are between the original and new positions of the x-word. Examples are given demonstrating how to identify hidden x-words like "does", "did", and "do" through various tests. The document concludes by mentioning compound sentences.