Which technique should you use to minimize down time while plugging this non-CDB into the CDB?

C – Transportable database is the correct answer.

B – Wrong as the database is 11.2.0.2

Ref: 12c New Features for Administrators

There are three possible methods to plug a non-CDB database into a CDB.
Whichever method is used, you have to get the non-CDB into a transactionally consistent
state and open it in restricted mode.
• Either use transportable tablespace (TTS) or full conventional export/import or
transportable database (TDB) provided that in the last one any user-defined object
resides in a single user-defined tablespace.
• Or use DBMS_PDB package to construct an XML file describing the non-CDB data files
to plug the non-CDB into the CDB as a PDB. This method presupposes that the non-
CDB is an Oracle 12c database.
• Or use replication with GoldenGate
Using the DBMS_PDB package is the easiest option.
If the DBMS_PDB package is not used, using export/import is usually simpler than using
GoldenGate replication, but export/import might require more downtime during the switch from
the non-CDB to the PDB.

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If you choose to use export/import, and you are moving a whole non-CDB into the CDB,
transportable databases (TDB) is usually the best option.
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If you choose to export and import
part of a non-CDB into a CDB, transportable tablespaces (TTS) is the best option.