What could be the reason?

View Exhibit1 and examine the indexes on the CUSTOMERS table.

The statistics for the CUSTOMERS table have been updated recently by using the following command:
SQL> EXEC DBMS_STATS.GATHER_TABLE_STATS(‘SH’,’CUSTOMERS’,method_opt=>’FOR
ALL
INDEXED COLUMNS SIZE AUTO’);
View Exhibit2 to examine a query plan. Even though the index is present on the COUNTRY_ID
and CUST_GENDER columns, the query uses a full table scan. What could be the reason?

A.
because the histogram statistics for the COUNTRY_ID column are not updated

B.
because the DB_FILE_MULTIBLOCK_READ_COUNT initialization parameter is set to a high
value

C.
because the optimizer calculates the cost of accessing blocks by using a full table scan to be
less as compared to index scans, even though indexes are available

D.
because indexes on CUST_GENDER and COUNTRY_ID columns are of different types, the
index on the CUST_GENDER column is bitmap index, and on COUNTRY_ID columns is btree
index.