Making outbound connection to the internet not successful

I am studying AWS and came across a question here:

After launching an instance that you intend to serve as a NAT (Network Address Translation) device in a public subnet you modify your route tables to have the NAT device be the target of internet bound traffic of your private subnet When you try and make an outbound connection to the internet from an instance in the private subnet, you are not successful. Which of the following steps could resolve the issue?

NAT device is the target of internet bound traffic of your private subnet When you try and make an outbound connection to the internet from an instance in the private subnet, you are not successful. Which of the following steps could resolve the issue?

A. Disabling the Source/Destination Check attribute on the NAT instance
B. Attaching an Elastic IP address to the instance in the private subnet
C. Attaching a second Elastic Network Interface (ENI) to the NAT instance, and placing it in the private subnet
D. Attaching a second Elastic Network Interface (ENI) to the instance in the private subnet, and placing it in the public subnet

I thought B is the right answer but it seems I am wrong, can anyone enlighten me with the right answer?

Thank you very much.

Solution

A) Disabling the Source/Destination Check attribute on the NAT instance

Each EC2 instance performs source/destination checks by default. This means that the instance must be the source or destination of any traffic it sends or receives. However, a NAT instance must be able to send and receive traffic when the source or destination is not itself. Therefore, you must disable source/destination checks on the NAT instance.

You can disable the SrcDestCheck attribute for a NAT instance that's either running or stopped using the console or the command line.

https://docs.aws.amazon.com/vpc/latest/userguide/VPC_NAT_Instance.html#EIP_Disable_SrcDestCheck