Answer: B — To secure the loan for the lender.
Collateral is an asset used as a guarantee; if the borrower fails to repay, the lender can sell it to obtain payment.
The passage explicitly states collateral is a "guarantee to a lender until the loan is repaid" and the lender can sell it if the borrower defaults — making option B the only correct answer. Options A, C, and D are not mentioned and contradict the text.