Determine the shear stress required to move the single grain on the side slopes, if the critical shear stress required moving the similar grain on the horizontal bed is 2.91 N/m². Consider the angle of the side slope with the horizontal as 30° and the angle of repose of soil as 37°.

• A. 1.61 N/m²
• B. 2.61 N/m²
• C. 2.91 N/m²
• D. 1.00 N/m²