From the given options, select the word that correctly substitutes the expression-

“Event that serves as an introduction”

Prologue

The word that correctly substitutes the expression "event that serves as an introduction" is prologue.

• Epilogue is a concluding event or statement.
• Post-Script is a message added after the main text of a letter or document.
• Summary is a brief statement of the main points of something.

A prologue is an introductory event or statement that comes before the main part of a story. It is often used to set the scene or introduce the characters.