Which of the following statements about rebuilding an index is true?

A.
The NOLOGGING and ONLINE keywords can never be used together.

B.
Without the ONLINE keyword the index is locked for any DML operation.

C.
The NOLOGGING and ONLINE keywords are always usedtogether.

D.
Without the ONLINE keyword the index is locked for the SELECT operation.

Explanation:
The syntax of the REBUILD command has many options such as TABLESPACE, ONLINE, and NOLOGGING.
The discussion is narrowed down to
ONLINE and NOLOGGING options. NOLOGGING disables redo generation only for the index rebuild; all
subsequent DML against the index will
generate redo as normal. Without the ONLINE keywordthe index is locked for DML, but not for SELECT.
However, the rebuild still continues.