The correct configuration for static NAT to allow HTTP access to a web server through two different ISPs involves using the 'extendable' keyword. This keyword allows the router to create multiple entries for the same local or global address. In this case, it enables the web server to beaccessible via both ISP 1 and ISP 2. The 'extendable' option is necessary because without it, the router would not accept a second NAT entry with the same local IP and port, which is required for accessibility through both ISPs.