C) Data is safe in case of disaster is the main advantage of off-site backup. If your data is backed up off-site, then it is safe in the event of a disaster such as a fire, flood, or other natural disaster.
A) There may be less bandwidth usage because the data is not stored on-site, but this is not necessarily a primary advantage of off-site backup.
B) Access to data may not necessarily be quicker with off-site backup, as it depends on the speed of the connection and the location of the off-site backup.
D) Data is not necessarily more secure because of less outbound traffic, as security depends on the measures taken to protect the data, not just the amount of traffic.