<span>The subject tells what the sentence is about; it contains the main noun or noun phrase. </span>
I hope this is a good explanation.
Things that happen in a story can help you find out the theme, like if a character does something and lies about it, and then other characters find out and that first character gets consequences, then the theme of the story is to not lie.
Introductions in any form of writing greatly affect the readers interest about the writing and also it gives them ideas what is the content of the text. In an essay, sometimes the writer would ask question, explain thoughts or use catchy phrase in order to gain interest of the reader to read their essays
