C - I believe the question implies that the criteria for the two territories is the same and what is the *issue* vs. what is the *solution*.

Apex code that has the same criteria for both is not going to solve any issue.

The territory with the highest territory type priority is automatically assigned to the opportunity when an account meets criteria for multiple territories4.
Option A is incorrect, since creating a process builder process to update the territory field on the opportunity would be unnecessary and complex.
Option C is incorrect, since creating an Apex class that implements Filter-Based Opportunity Territory Assignment would be an advanced and custom solution that is not required in this scenario.
Option D is incorrect, since creating a criteria-based sharing rule on the opportunity to assign it to a territory would not work, as sharing rules do not assign territories5.

D. Create an Apex class that implements Filter-Based Opportunity Territory Assignment.

Enterprise Territory Management (ETM) in Salesforce allows for the automatic assignment of accounts (and related opportunities) to territories based on assignment rules. However, when an account qualifies for multiple territories, as in the case of an account that meets criteria for both Portugal and Southern Europe territories, Salesforce does not automatically assign opportunities to a territory based on territory type priority or other criteria out-of-the-box.

For such scenarios where complex logic is needed to determine the appropriate territory assignment for opportunities—especially when they might fall into multiple territories—custom logic through Apex is required. By creating an Apex class that implements filter-based opportunity territory assignment, you can define specific rules or criteria to decide how opportunities are assigned to territories, considering factors like territory type priority, geographic location, or other custom criteria relevant to the business process.

This approach provides the flexibility to manage complex territory assignment requirements that cannot be handled through standard configuration options in Salesforce ETM....

D. Create an Apex class that implement. Filter-Based Opportunity Territory Assignment

https://www.infallibletechie.com/2016/11/how-does-filter-based-opportunity.html?expand_article=1

https://resources.docs.salesforce.com/latest/latest/en-us/sfdc/pdf/salesforce_implementing_territory_mgmt2_guide.pdf

Enterprise Territory Management in Salesforce allows you to model your sales territories based on criteria such as geography, industry, product line, and more. By default, accounts are assigned to territories based on these criteria, but opportunities are not.

To assign opportunities to territories, you can use Apex to create a class that implements Filter-Based Opportunity Territory Assignment. This class can define custom logic to assign opportunities to the correct territories based on your business needs.