Which of the following statements is not correct?

a. The more selective a query predicate’s FF, the less desirable it is to use the index on the corresponding attribute type in the access plan.

b. For range queries, a primary or clustered index is more efficient than a secondary index.

c. The number of block accesses determines the performance, not the number of rows retrieved.

d. The more attribute types are included in the index, the higher the performance impact is on update queries.