Final answer:
The third column type required to enable Card View, along with dropdown list and symbol columns, is the Contact List column.
Step-by-step explanation:
To enable Card View in a spreadsheet or project management tool, it is required that your sheet includes at least one of three specific column types. You correctly identified two of those columns as the dropdown list and symbol columns. The third column type that you need for enabling Card View is a Contact List column. This column type helps in assigning tasks or items to specific individuals, and it's crucial for many card-based systems because it facilitates sorting and organizing information by person assigned.