Choice "B" is correct. The AICPA's Statements on Quality Control Standards assert that a system of quality control for a firm encompasses the firm's organizational structure and the policies and procedures established by the firm in order to provide reasonable assurance of conforming to professional standards. Toward that end, policies and procedures for human resources, including assigning personnel to engagements, should be established to provide reasonable assurance that the persons assigned will have the technical training and proficiency required to perform their work and progress within the firm.
Choice "d" is incorrect. Compliance with laws and regulations falls under the Code of Professional Conduct.
Choice "a" is incorrect. The use of statistical sampling techniques involves auditing standards, not standards of quality control.
Choice "c" is incorrect. The consideration of audit risk and materiality involves auditing standards, not standards of quality control.