You decide to set up Cloud NAT. After completing the configuration, you find that one of your instances is not using the Cloud NAT for outbound NAT. What is the most likely cause of this problem? 

Answer options:

A. The instance has been configured with multiple interfaces. 
B. An external IP address has been configured on the instance. 
C. You have created static routes that use RFC1918 ranges.
D. The instance is accessible by a load balancer external IP address.

B

Reference: https://www.sovereignsolutionscorp.com/google-cloud-nat/