Explanation/Reference:
A: An Exadata snapshot database can be either a non-container database (non-CDB) or a container database (CDB). Creating an Exadata snapshot database of a CDB enables access to all of the pluggable databases in that container.
C: You can create two types of Exadata snapshots, depending on the current setup of your environment:
You have a pluggable database (PDB) and want to create a test master from it.

You have a container database (CDB) and want to create test masters from all its PDBs, or you have a

simple non-container database and want to create a test master from it.
D: SPARSE disk group based database snapshots is functionality included in Exadata Storage Software. It requires Exadata Storage Software version 12.1.2.1.0 and Oracle Database 12c version 12.1.0.2 with bundle patch 5 or later. This feature is designed to work on native Exadata ASM storage disk groups. It uses ASM SPARSE grid disk based thin provisioning where snapshot databases created on a SPARSE disk group need only the space for changes plus some metadata, thereby enabling storage efficient snapshot databases.
References:
http://docs.oracle.com/cd/E80920_01/SAGUG/exadata-storage-server-snapshots.htm#SAGUG-GUID- E1D6EF45-36EF-40E3-A57E-F80B749E6122
http://www.oracle.com/technetwork/database/exadata/learnmore/exadata-database-copy-twp-2543083.pdf