A Company Has Created a VPC with Multiple Private Subnets

A company has created a VPC with multiple private subnets in multiple Availability Zones (AZs) and one public subnet in one of the AZs. The public subnet is used to launch a NAT gateway. There is instance in the private subnet that use a NAT gateway to connect to the internet. In case of an AZ failure, the company wants to ensure that the instance is not all experiencing internet connectivity issues and that there is a backup plan ready. Which solution should a solutions architect recommend that is MOST highly available?

A) Create a new public subnet with a NAT gateway in the same AZ. Distribute the traffic between the two NAT gateways.
B) Create an Amazon EC2 NAT instance in a now public subnet. Distribute the traffic between the NAT gateway and the NAT instance.
C) Create public subnets. In each AZ and launch a NAT gateway in each subnet. Configure the traffic from the private subnets in each AZ to the respective NAT gateway.
D) Create an Amazon EC2 NAT instance in the same public subnet. Replace the NAT gateway with the NAT instance and associate the instance with an Auto Scaling group with an appropriate scaling policy.