Which of the following is an example of a norm rather than a rule?

A general mandatory guideline asking all employees to leave their work machines in good order

A specific mandatory guideline asking employees to oil machine parts labeled A and $B$; and replace $C$ and $D$

An informal code of conduct recommending that employees help each other if time permits

A recommendation by the HR department that employees wear formal clothes during the week

A suggestion by the technical department that all work$-$related files are saved in a common location