D is incorrect, proved by experience.
E is incorrect:
https://docs.oracle.com/en/database/oracle/oracle-database/12.2/tgsql/optimizer-statistics-advisor.html#GUID-6D8831EA-B478-4641-B84B-C341BB4D0799
When feasible, recommendations have corresponding actions.
B is correct
https://docs.oracle.com/database/121/TGSQL/tgsql_optcncpt.htm#TGSQL218
The cost of an index scan depends on the levels in the B-tree, the number of index leaf blocks to be scanned, and the number of rows to be fetched using the rowid in the index keys. The cost of fetching rows using rowids depends on the index clustering factor.
A is incorrect, the number of blocks is considered instead of the number of rows.
The cost of the scan depends on the number of blocks to be scanned and the multiblock read count value.
AC
obviously DBMS_STATS not always produce good statistics, especially with default options/prefs.
A is not quite accurate, since cost does depend on selectivity for predicates/filters, which in turn depends on row num
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