In your test database， you have created the ORDERS table as an index­organized table （IOT）. To facilitate faster querying， you have created a mapping table and a bitmap index on the ORDER_FILLED column. You observe that the query performance degrades when users perform a large volume of transactions. 
While investigating the reason， you find that the mapping table segment is fragmented， leading to poor performance. Which option would you use to defragment the mapping table without affecting the original table data？（）

A.export and import the mapping table
B.drop and re­create the mapping table
C.truncate the mapping table and reinsert the values
D.use the ALTER TABLE .. REBUILD command to defragment the mapping table