Which of the following statements is correct?

a. SQL is a declarative language, meaning that the programmer has to specify which data to retrieve and how the data are to be located and retrieved from the physical database files.

b. The filter factor of a predicate is the fraction of rows that contain a missing value for that predicate.

c. If no further statistical information about a predicate is available, the filter factor of that predicate can be estimated by dividing 1 by the number of different values the attribute type can have.

d. Table cardinality is another way of referring to the number of columns in a table.