The -sV option in Nmap enables version detection, allowing the scanner to identify the version of the services running on the scanned ports. It tries various techniques to determine this information and is a key step in vulnerability scanning to identify potentially exploitable services. The -A option is also correct since it includes version detection among other advanced features, but it is not the most specific answer to the question. The -sS option performs a stealthy SYN scan but does not gather version information. The -O option is used for operating system detection, not service version detection.