Choice "C" is correct.  For a security interest to be enforceable, it must attach to the collateral.  There are three prerequisites to attachment, and all three must be satisfied for an interest to attach: (i) the parties have to agree to create a security interest, and this agreement must be evidenced either by the creditor's taking possession of, or having control of, the collateral or by a written security agreement describing the collateral and authenticated (e.g., signed) by the debtor, (ii) the secured party must have given value in exchange for the security interest, and (iii) the debtor must have rights in the collateral.Choice "a" is incorrect. All three prerequisites are required in order for a security interest to be enforceable.  A contract granting a security interest in collateral is not sufficient. Choice "d" is incorrect. As stated above, all three prerequisites are required.  This choice mentions the security agreement (one prerequisite) and filing, which is a method of perfection but is not a prerequisite to attachment. Choice "b" is incorrect. Again, all three prerequisites are required.  This choice mentions the existence of only one requirement, the security agreement.  Thus, choice "C" is the better choice.