The correct answer is 'read -p "Enter the file name: " file; IFS= read -r line < "$file"' because the '-p' option allows the script to prompt the user with a message and read input into the 'file' variable. Then, 'IFS= read -r line < "$file"' is used to read the first line from the file specified by the user into the variable 'line'; 'IFS=' prevents leading/trailing whitespace from being trimmed, and '-r' prevents backslashes from being interpreted as escape characters. The '< "$file"' syntax redirects the contents of the file into the read command. Options B and C are incorrect because they attempt to use 'cat', which is unnecessary and will not properly assign the first line to the variable 'line'. Option D is incorrect because '<<<' is not the correct way to redirect file content to 'read'.