Even though the number of parties is set to two in any action, each party may be comprised of multiple persons. This joinder may result from either procedural or substantive reasons. According to article 57 of the CoCP, multiple persons may jointly file an action or an action may be filed jointly against multiple persons if the right or the obligation that is the subject matter of the action between the plaintiffs or defendants is shared upon a reason other than joint ownership. This is known as the joinder of parties. The correct answer is B.