The correct answer is B, use data classification metadata fields available in field definition. Data classification metadata fields are standard fields that allow you to classify the sensitivity level of your data based on your organization's policies. You can use these fields to indicate whether a field contains confidential, restricted, or general data. These fields are available for both standard and custom objects in Salesforce. Using app exchange products, creating a custom picklist field, or building reports would not be as effective or consistent as using data classification metadata fields.