多项选择题 Which three features work together, to allow a SQL statement to have different cursors for the samestatement based on different selectivity ranges?（）

多项选择题 You notice a high number of waits for the db file scattered read and db file sequential read events in the recent Automatic Database Diagnostic Monitor (ADDM) report. After further investigation, you find that queries are performing too many full table scans and indexes are not being used even though the filter columns are indexed. Identify three possible reasons for this.（）

单项选择题 Which statement is true concerning dropping a pluggable database (PDB)?（）