The correct answer is: B. Files can not be kept inside a directory.
A directory is a container for files and other directories. It is a way of organizing files on a computer. Files can be stored in a directory, but directories cannot be stored in a file.
Option A is incorrect because directories cannot be kept inside a file.
Option C is incorrect because 1 millisecond is equal to 0.001 seconds, not 1000 seconds.
Option D is incorrect because only option B is correct.