Which of the following is the most accurate definition of the term ‘a floating charge’?

Is it

(a) An agreement to buy foreign currency at a fixed future date at an agreed price.

(b) A procedure applied for accounting records at the end of the accounting period to ensure that all transactions for the period have been recorded.

(c) A type of sales contract used in the computer software industry.

(d) Security taken by a lender that crystallises over a range of assets if the security is required.