Final answer:
In a RACI model, Responsible roles are necessary as they are the ones doing the work, and the Accountable role is required as this person has ultimate authority and responsibility for the completion of the task.
Step-by-step explanation:
Within the RACI model, which stands for Responsible, Accountable, Consulted, and Informed, certain roles are considered necessary whereas others are required. The RACI model is a responsibility assignment matrix that is used to delineate the roles and responsibilities in a task, project, or process.
The correct answer to the question is B. Necessary - Responsible, Required - Accountable. In the RACI model, Responsible refers to those who do the work to achieve the task. They are the ones who must complete the task or make the decision. There can be multiple people responsible, but there should be exactly one person who is Accountable for each task. The Accountable person is the individual who is ultimately answerable for the activity or decision, and this includes yes or no authority and veto power.
The other two aspects, Consulted and Informed, are important as well. Consulted refers to those whose opinions are sought; typically they are subject matter experts. Meanwhile, Informed refers to those who are kept up-to-date on progress, often only upon the completion of the task or decision. It's crucial that in a RACI matrix, every role is clearly defined to prevent confusion and ensure that tasks are completed efficiently.