The unix system does not attempt to avoid cycles. instead, it restricts access to the linking capability of the system. normal users may only create hard links to files, but not to this prevents normal users from inadvertently creating cycles.

a) files in use
b) directories
c) root folders
d) working folders

b) directories

Explanation:

Based on the information provided it can be said that Normal users may only create hard links to files, but not to directories. These are locations addresses used for storing files within a computer, and are used in various operating systems such as Linux, OS/2 and UNIX. Like mentioned in the question, by preventing access to directories when creating hard links it prevents cycles from being created inadvertently.

you are welcome for my answer it is b⇔⇒⊕