Sales Ops has requested from the Salesforce Admin to display the account primary segment field on all opportunities. How would the Salesforce Admin achieve this?

Answer options:

A.Create a Process Builder that will update all opportunities with the account primary segment
B.Create a validation rule that will reference the account primary segment
C.Add the account primary segment field through the opportunity page layout
D.Create a formula field on the opportunities that will reference the account primary segment

Correct Answer: D 
You can create a formula field on the opportunity so every change in the account field will be visible on the opportunity. Formula fields are real-time and will reflect the changes right away. Formulas can help you to automatically calculate the value of a field based on other fields.Because formula fields are automatically calculated, they are read-only on record detail pages and do not update last modified date fields. Formula fields are not visible on edit pages. 
Option A is incorrect because the process builder doesn’t work real-time and will not reflect the changes right away. 
Option B is incorrect because the validation rule doesn’t have the option to do any field update. 
Option C doesn’t have a way to show that the value of the field will be updated. Creating a field only doesn’t help. 
Reference: 

https://success.salesforce.com/answers?id=9063A000000e1SuQAI