12. the transformation from (4, p) to (a, p) is canonical when the following condition is satisfied. (a) (p,dq +pdq,) is an exact differential (b)pda -pdq,) is

12. The transformation from (4, p) to (a, P) is canonical when the following condition is satisfied. (A) (P,dQ +pdq,) is an exact differential (B)Pda -pdq,) is an exact differential (C)2(Pdq -pdo,) is an exact differential (D)2Pdp-Qdq) is an exact differential