Total substitution of a new contract in place of an old one takes place in the case of

Novation is the complete substitution of a new contract in place of an old one, discharging the original contract entirely. It requires mutual agreement and can involve changing parties (new debtor replaces old) or changing terms. Remission (A) reduces obligation, recission (B) cancels for fraud/mistake, alteration (D) modifies terms - none involve total substitution like novation.