Which of the following statements about domain constraints in a relational database is most accurate?

1. ADomain constraints automatically enforce referential integrity between primary and foreign keys.
2. BDomain constraints ensure that each attribute's value belongs to a predefined set or type, and may restrict NULL values if specified.
3. CDomain constraints apply only to numeric attributes and are ignored for character or date types.
4. DDomain constraints define relationships between multiple attributes across different tables.