Choice "D" is correct. Attachment of a security interest takes place when three events have been completed:

1. Agreement between creditor and debtor (or the creditor has either possession of or control of the collateral),

2. Value is given by creditor, and

3. Debtor has rights in collateral

Here, attachment took place when the loan was made and the debtor signed the security agreement.Choice "c" is incorrect. The filing of a financing agreement is not a requirement for an "attachment."
Choice "a" is incorrect. "Perfection" here would require the filing of the financing statement; although a small scale assignment of accounts is automatically perfected, here the assignment was of all of Pix Co.'s accounts.
Choice "b" is incorrect. A security interest in intangibles, such as accounts receivable, can be perfected. However, "perfection" did not occur here because there was no filing.