In a formal discussion the focus is often on facts or evidence. there are no specific, agreed-upon rules. one person does not typically lead others. personal feelings and stories are the focus.

The best answer is "The focus is often on facts or evidence"
A formal discussion does include specific, agreed-upon rules, implied or otherwise. Consider that one cannot curse, or should not curse, in a formal discussion.
One person may lead a formal discussion, and often does. Think of a moderator in a debate, the manager running a meeting with her employees, etc.
Personal feelings and stories are not generally the focus of a formal discussion.
A formal discussion should generally be fact-based and emotions should be put to the side. 

Aand c is your answer btw your welcome