The correct answer is A: In the security group of the EC2 instance, allow inbound ICMP traffic. The reason is that security groups are stateful, meaning that if you allow inbound ICMP traffic, the response traffic will also be automatically allowed. NACLs (Network ACLs) are stateless, meaning you would need to create rules for both inbound and outbound traffic; however, typically issues with ICMP traffic not being allowed are due to security group configurations not permitting inbound traffic. Therefore, ensuring that the security group allows inbound ICMP traffic should resolve the issue.