Possible to drop a PDB without unplugging it. The PDB must be in MOUNT stage.

Enterprise Database Express is available only when the database is open. This mean that Enterprise Manager Database Express can not be used to startup the database and other operations that require that the database change state, such as enable, disable ARCHIVELOG mode, are also not available in Enterprise Database Express.

Explanation
You must specify the names and locations of the seed's files in one of the following ways:
* (A) Oracle Managed Files
* (B) The SEED FILE_NAME_CONVERT Clause
* (C) The PDB_FILE_NAME_CONVERT Initialization Parameter

ENABLE_DDL_LOGGING enables or disables the writing of a subset of data definition language (DDL) statements to a DDL alert log.
The DDL log is a file that has the same format and basic behavior as the alert log, but it only contains the DDL statements issued by the database. The DDL log is created only for the RDBMS component and only if the ENABLE_DDL_LOGGING initialization parameter is set to true. When this parameter is set to false, DDL statements are not included in any log.

A:You can create and rebuild indexes online. Therefore, you can update base tables at the same time you are building or rebuilding indexes on that table. You can perform DML operations while the index build is taking place, but DDL operations are not allowed. Parallel execution is not supported when creating or rebuilding an index online.
B: Note: *Transporting and Attaching Partitions for Data Warehousing Typical enterprise data warehouses contain one or more large fact tables. These fact tables can be partitioned by date, making the enterprise data warehouse a historical database. You can build indexes to speed up star queries. Oracle recommends that you build local indexes for such historically partitioned tables to avoid rebuilding global indexes every time you drop the oldest partition from the historical database. D:Moving (Rebuilding) Index-Organized Tables Because index-organized tables are primarily stored in a B-tree index, you can encounter fragmentation as a consequence of incremental updates. However, you can use the ALTER TABLE...MOVE statement to rebuild the index and reduce this fragmentation.