To add a Cisco Secure Firewall Threat Defense (FTD) device to Cisco Secure Firewall Management Center (FMC), the correct command to use is configure manager add 192.168.75.201 <reg_key>. This command registers the FTD device with the FMC using the FMC's IP address and the registration key provided during the FMC setup.
Command structure:
* configure manager add <FMC_IP> <reg_key>
For the given scenario:
* FMC IP address: 192.168.75.201
* Registration key: provided during FMC setup
Thus, the correct command is:
* configure manager add 192.168.75.201 <reg_key>
References: Cisco Secure Firewall Management Center Device Configuration Guide, Chapter on Device Registration.