An org has a requirement that addresses on Contacts and Accounts should be normalized to...

In software engineering, the DRY (Don't Repeat Yourself) principle is fundamental for maintainability. If the logic for normalizing an address is identical for both Accounts and Contacts, that logic should not be duplicated across two separate trigger files.

The optimal implementation (Option D) is to create a single Trigger Helper or Utility class. This class contains a static method (e.g., AddressService.normalize(List records)) that performs the normalization logic. You then create a small trigger on the Account object and a small trigger on the Contact object, both of which simply invoke this shared helper method.

This approach offers several advantages:

Maintainability: If the company standard for addresses changes (e.g., changing "St." to "Street"), the developer only needs to update the code in one place.

Reusability: The helper method can also be called from other contexts, such as an Anonymous Apex script or a Batch job.

Readability: Triggers remain "thin" and easy to read, acting only as entry points rather than containing complex business logic.

Options B and C are technically impossible; a trigger on one object cannot "call" a trigger on another object directly. Option A is less optimal because it leads to code duplication and a higher risk of bugs when logic is updated in one trigger but forgotten in the other.