In analysis of mechanical stresses, which of the following is the correct form of the 3D equation of stress equilibrium?

• A. ( frac{ partial sigma x}{ partial x}+ frac{ partial tau xy}{ partial y}+ frac{ partial tau xz}{ partial z} )=0
• B. ( frac{ partial tau xy}{ partial x}+ frac{ partial sigma y}{ partial y}+ frac{ partial tau yz}{ partial z} )=0
• C. ( frac{ partial tau xz}{ partial x}+ frac{ partial tau yz}{ partial y}+ frac{ partial sigma z}{ partial x} )=0
• D. No such equation exists