The momentum equation is ( rho frac{Du}{Dt}=- frac{ partial p}{ partial x}+ frac{ partial tau_{xx}}{ partial x}+ frac{ partial tau_{yx}}{ partial y}+ frac{ partial tau_{zx}}{ partial z}+ rho f_x ). Which of these statements about sign convention can be inferred from this equation?

• A. Pressure force is taken as negative
• B. Tensile force is taken as negative
• C. Pressure force is taken as positive
• D. Pressure force is unsigned