Answer – C
The following are the key distinctions between NAT Instances and NAT gateways
NAT Gateways
NAT Instances
Highly available. NAT gateways in each Availability Zone are implemented with redundancy. Create a NAT gateway in each Availability Zone to ensure zone-independent architecture
Use a script to manage failover between instances.
Supports bursts of up to 10Gbps.
Depends on the bandwidth of the instance type.
Managed by AWS.You do not need to perform any maintenance.
Managed by you, for example, by installing software updates or operating system patches on the instance.
Cannot be associated with a NAT gateway. You can associate security groups with your resources behind the NAT gateway to control inbound and outbound traffic.
Associate with your NAT instance and the resources behind your NAT instance to control inbound and outbound traffic.
For more information on the comparison, please visit the link:
http://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/vpc-nat-comparison.html