The fundamental requirement is to grant marketers access to the Opportunity object. In Salesforce, access to objects is controlled by Object Permissions, which are defined on a user's profile. The standard "Marketing User" profile does not include permissions for the Opportunity object. While standard profiles cannot be edited directly, the standard administrative practice is to clone a standard profile and then modify the clone to meet specific business requirements. Therefore, the correct next step is to edit the object permissions on the marketers' (cloned) profile to grant the required access to Opportunities.

B. Add a custom permission set to include Opportunity.

While a permission set is a valid way to grant access, editing the profile is a more direct approach if all users with that profile require the same permissions, as implied here.

C. Edit the role to enable Sales access.

Roles control record-level visibility (which specific records a user can see) through the role hierarchy, not the fundamental permission to access an object itself.

D. Configure the assigned apps to include Opportunity.

Assigned apps control which applications and associated tabs are visible to a user in the App Launcher. This does not grant the underlying object-level permissions required to view or edit records.

1. Salesforce Help & Training, "Control Access to Objects": "The first level of data access is objects. Object-level security provides the simplest way to control which users have access to which data... You set object permissions in profiles and permission sets." This confirms that object access is managed via profiles/permission sets.

2. Salesforce Help & Training, "Standard Profiles": "You can’t edit the object, user, and field permissions on a standard profile." This documentation implicitly supports the common practice of cloning a standard profile before editing its permissions, making option A the logical subsequent action.

3. Salesforce Trailhead, "Data Security" Module, "Control Access to Objects" Unit: "Object permissions determine the baseline level of access for all the records in an object... You can manage object permissions in profiles and permission sets." This reinforces that the core task is to modify object permissions, which is most directly stated in option A.