The correct answer is: A. Prologue : Epilogue
A propensity is a natural tendency or inclination to do something. A tendency is a natural inclination or disposition towards a particular action or course of behavior. A prologue is an introductory section or speech that comes before the main part of a book, play, or film. An epilogue is a concluding section or speech that comes after the main part of a book, play, or film.
In both cases, the first word describes something that comes before the second word. A propensity is a tendency that comes before an action, and a prologue is an introductory section that comes before the main part of a book.
The other options do not have the same relationship. A master is someone who has control over a slave, while audacity is boldness or daring. Conduct is behavior, while immorality is wickedness or evil.