Which situation is considered a data breach according to the GDPR?

Which situation is considered a data breach according to the GDPR?
A . A processor deletes personal data after his contract with the controller expired.
B . A processor leaves his computer unattended, where colleagues may be able to access it.
C . After a disk crash a processor restores personal data from a recent back-up.
D . After processing a processor deletes personal data on instruction of the controller.

Answer: B