What is an example of an implicit rule?

Multiple Choice

a company$-$wide email prohibiting employees from discussing the details of a client agreement

an unspoken expectation that meeting attendees remain quiet while any team member is presenting

a supervisor who says, "I expect you all to keep the conversation civil"

a line in the employee handbook forbidding the use of personal email accounts on company time

a sign that says $"$No cell phone use in the lobby"