1. Mapping a relationship that has a total participation, implies that the foreign key should be: a. Unique b. Not null c. Duplicated d. none of the above 2. The data of a composite key may be as follow: a. a partial key may have null value and the others not b. a partial key may have duplicated value c. at least one partial key should be unique d. none of the above Index which has an entry for secondary key value is classified as a. hashing index b. dense index 3. c. non dense index d. cluster index