Final answer:
Filters that can include an 'Add Constraint' are often related to specific actions, demographic, or firmographic criteria. For example, filtering by 'Filled out form', 'Industry', or 'Number of Employees' can include constraints tied to particular details or ranges within those categories.
Step-by-step explanation:
Among the options provided (A. Filled out form, B. Industry, C. Number of Employees, D. Member of Smart List), filters that can typically include an "Add Constraint" are related to actions or behaviors (such as 'Filled out form') and demographic or firmographic criteria (such as 'Industry' or 'Number of Employees'). Whether a 'Member of Smart List' can include an 'Add Constraint' depends on the specific tools or systems you're using, but in many marketing automation platforms, this is a possibility.
For example, when you filter by 'Filled out form', you can add constraints like the specific form name, the date it was filled out, or the number of times it was filled out. Similarly, when using 'Industry' as a filter, you might want to add constraints based on certain sectors or sizes of the industry. 'Number of Employees' can also be constrained to a certain range or type of company sizes.