"A" will syncronise passwords between on pre-mise and the GCP, this duplicates the existing strategy plus Google's "built-in" encryption of
all the data. "B" does not support the moving to GCP. "C" The directory sync tool copies the filesystem settings between servers, UNIX filesystems
have permission settings built in and passwords to log into the permission groups, syncing these would set GCP up the same way their on-premises
is, plus Google's "built-in" encryption. "D" disrupts the users, so this is not correct. The debate should be between "A" and "C", "C" includes
"A" according to (https://cloud.google.com/solutions/migrating-consumer-accounts-to-cloud-identity-or-g-suite-best-practices-federation) so
choose "C"