Consider the turbulent structure of thin shear layers. Which of these statements is correct?

• A. The rates of change of the flow variables are very high in every direction
• B. Flow variables do not vary much in any direction
• C. The rates of change of the flow variables in the cross-sectional direction are smaller than that of the flow direction
• D. The rates of change of the flow variables in the flow direction are smaller than that of the cross-sectional direction