Generally,a security interest is perfected when the:

A) secured party has done everything that the law requires to give the secured party greater rights to the goods than others have.
B) secured party has a legally enforceable right to take that property and sell it to satisfy the debt.
C) buyer takes the property subject to a mortgage and the seller agrees to continue paying the debt.
D) goods are sold,but regained as soon as the debtor takes possession of the new property.

Perfection of a security interest refers to the process of giving the secured party greater rights to the collateral than any other creditor of the debtor. This is typically done by complying with the requirements of the applicable state law, such as filing a financing statement or taking possession of the collateral. Once perfected, the security interest is enforceable against third parties and the secured party has the right to take possession of and sell the collateral to satisfy the debt if necessary. None of the other options in the question describe the process of perfection of a security interest.