Choice "B" is correct. Because a holder in due course of a negotiable instrument has priority over a prior perfected security interest, the best way to perfect a security interest in a negotiable instrument is to take possession of it, because taking possession of the instrument prevents a later person from becoming a holder in due course. Choice "c" is incorrect. A security interest perfected by filing may be defeated by a subsequent holder in due course, so filing is not the best method of perfecting here.Choice "d" is incorrect. A security interest in a negotiable instrument is not automatically perfected upon attachment, as this choice suggests, so relying on attachment would be wholly ineffective. Choice "a" is incorrect. Merely obtaining an executed financing statement is not a method of perfection; the statement must be filed to constitute perfection. Moreover, as discussed with respect to choice "B", filing is not the best method of perfecting when a negotiable instrument is involved because a subsequent holder in due course would have higher priority.