Which of the following relationships is valid only for reversible process undergone by a closed system of simple compressible substance (neglect changes in kinetic and potential energy?
(a) 
$\delta Q$ = $\delta$u + $\delta$W
(b) T dS = dU + p dV
(c) T dS = dU + 
$\delta$W
(d) 
Q = dU + p dV