Identify A, B, C and D in the following sequence of reactions:
`C_(2)H_(5)OH underset(H_(2)SO_(4))overset(K_(2)Cr_(2)O_(7))to A overset([O])to B overset(NH_(3))to C overset("Heat")to D`

Explanation

`C_(2)H_(5)OH underset(H_(2)SO_(4))overset(K_(2)Cr_(2)O_(7))to underset((A))(CH_(3)CHO) overset([O])to underset((B))(CH_(3)COOH) overset(NH_(3))to underset((C))(CH_(3)COO^(-)NH_(4)^(+))overset(Delta)to CH_(4)(D)`