Reference Material:

https://docs.aws.amazon.com/elasticloadbalancing/latest/classic/x-forwarded-headers.html
X-Forwarded-For
The X-Forwarded-For request header is automatically added and helps you identify the IP address of a client when you use an HTTP or HTTPS load balancer. Because load balancers intercept traffic between clients and servers, your server access logs contain only the IP address of the load balancer. To see the IP address of the client, use the X-Forwarded-For request header. Elastic Load Balancing stores the IP address of the client in the X-Forwarded-For request header and passes the header to your server. If the X-Forwarded-For request header is not included in the request, the load balancer creates one with the client IP address as the request value. Otherwise, the load balancer appends the client IP address to the existing header and passes the header to your server
For me, this parameter is available on ELB, so we simply can enable ELB Access logs and get it. So B can be chosen?