Static external IP addresses are:

Answer options:

A.Global resource
B.Regional resource
C.Zonal resource
D.Either A or B

Correct Answer: D
Static external IP addresses can be either a regional or a global resource. A regional static IP address lets resources of that region or resources of zones within that region use the IP address. In this case, VM instances and regional forwarding rules can use a regional static IP address.
Global static external IP addresses are available only to global forwarding rules, which are used for global load balancing. You can not assign a global IP address to a regional or zonal resource like a Compute Engine instance.
Option A is incorrect. Static external IP addresses can be regional resources also.
Option B is incorrect. Static external IP addresses can be global resources also.
Option C is incorrect. VM instances and disks are examples of Zonal resources.
Option D is correct because a Static external IP address can be either a regional or a global resource.
Reference:
https://cloud.google.com/compute/docs/ip-addresses