In a nested directory structure, the 'find' command line option that would be used to restrict the command to searching down a particular number of subdirectories is '-maxdepth'. The 'find' command is used to search for files and directories based on various criteria, such as name, size, type, and modification time. The '-maxdepth' option is used to specify the maximum depth to which the 'find' command will descend. For example, to search for files with a '.txt' extension in the current directory and its subdirectories, but not in any deeper subdirectories, you can use the following command: find . -maxdepth 1 -name "*.txt" This command will search for files with a '.txt' extension in the current directory and its subdirectories, but will not search any deeper.