Final answer:
The correct nmap command to import a list of hosts from a file is 'nmap -iL /tmp/'. The -iL flag is designed to read a list of target specifications from a file provided by the user, such as 'nmap -iL /tmp/filename.txt'.
Step-by-step explanation:
The correct command line to import a list of hosts from a file for scanning with nmap is nmap -iL /tmp/. The -iL flag tells nmap to read the list of target specifications from a file. It is important to include the file name after the /tmp/ path, like nmap -iL /tmp/filename.txt, where filename.txt represents the actual file containing the list of hosts.