Answer: Control files, data files and redo log-files must be synchronized
Explanation:
While the process of opening of the database takes place , there is the certain requirement of acknowledging the state and instance of the database.This is a major step to start up the process and thus synchronization is done.
The synchronization process takes place in the control file, redo log-file and the data files.These files operate after the database is opened up or started.