The recommended solution to grant the customer service agent access to the field is creating a permission set that allows read-only access to the field via Field Level Security and assigning it to the agent. A permission set is a collection of settings and permissions that give users access to various tools and functions. Field Level Security (FLS) is a setting that controls the access level of fields for different profiles or permission sets. The app builder can create a permission set that grants read-only access to the custom field on the account object via FLS and assign it to the agent. Option B is incorrect because creating a new profile to allow for read-only access to the field via FLS and assigning it to the agent is not recommended, as profiles are used to define the baseline permissions and settings for a group of users, and creating multiple profiles for individual users can be hard to maintain. Option C is incorrect because updating the Customer Service Profile already assigned to the agent to allow for read-only access to the field via FLS is not recommended, as this will affect all users who have the same profile, which may violate the security policy. Option D is incorrect because updating the custom field’s FLS in setup to allow the agent read-only access to the field is not possible, as FLS can only be set at the profile or permission set level, not at the user level.