Regarding the description of the default security zone of the USG series of security firewalls, which is correct?

Regarding the description of the default security zone of the USG series of security firewalls, which is correct?
A . The default security zone can be deleted
B . The default security zone can modify the security level.
C . The default security zone cannot be deleted, but the security level can be modified.
D . There are 4 default security zones.

Answer: D