Which of these conditions is not met at a point for irrotational flow?

• A. ( frac { w}{ y} = frac { v}{ z} )
• B. ( frac { w}{ x} = frac { u}{ z} )
• C. ( frac { v}{ x} = frac { u}{ z} )
• D. ( frac { v}{ x} = frac { u}{ y} )