The true statement is: All folders are similar, but files can be quite different.
This is because folders (or directories) are typically used to organize and contain files, and they generally have similar properties and functionalities. On the other hand, files can vary greatly in content, format, size, and purpose.
The other statements are incorrect as they misrepresent the relationship between files and folders. Files are not a type of folder, nor are folders a type of file.