Select the option that can be used as a one-word substitute for the given group of words.
Words inscribed on a tomb.

The correct option is Epitaph.

Let's break down the meaning of the given phrase and analyze each option to understand why "Epitaph" is the correct one-word substitute:

1. Understanding the given phrase:
"Words inscribed on a tomb" refers to the short text written on a tombstone or monument in memory of a deceased person.

2. Analyzing the options:
• Epitaph: This noun specifically refers to a phrase or form of words written in memory of a person who has died, especially as an inscription on a tombstone. Therefore, this is the perfect match.
• Prologue: This refers to an introductory section of a literary, dramatic, or musical work.
• Epilogue: This refers to a section or speech at the end of a book or play that serves as a comment on or a conclusion to what has happened.
• Post-script: (Often written as postscript or P.S.) This is an additional remark written at the end of a letter, after the signature.

Thus, the appropriate one-word substitute for "words inscribed on a tomb" is Epitaph.