please answer these multiple choices . and please make sure to be correct . Thanks

CHAPTER 2: (Multiple Choice) Circle the correct answer (3 each 60 points) 21. A(n) s main function is to help one understand the complexities of the real-world environment. a. node b, entity c, model d. database 22. A(n) is anything about which data are to be collected and stored a, attribute b, entity 23. c, relationship d. constraint world. A(n) represents a particular type of object in the real a. attribute b, entity c, relationship d. node 24. A(n) the equivalent of a field in a file system. b, entity a, attribute c, relationship d constraint 25, A(n) s bidirectional. a, attribute b, entity c, relationship d, constraint 26, A(n) is a restriction placed on the data. a. attribute b, entity c, relationship d. constraint 27, are important because they help to ensure data integrity. a. Attributes b. Entities c. Relationships d. Constraints 28, are normally expressed in the form of rules. a. Attributes b. Entities c. Relationships d. Constraints