The instantaneous stream-wise velocity of a turbulent flow is given as follows:\(u\left( {x,\;y,\;z,\;t} \right) = \bar u\;\left( {x,\;y,\;z} \right) + u'\left( {x,\;y,\;z,\;t} \right)\)The time-average of the fluctuating velocity u’ (x, y, z, t) is

• A. u’/2
• B. \(- \bar u/2\)
• C. zero
• D. \(\bar u/2\)