Given a text T, and several options, according to the question posed in the text T to choose the most appropriate option from the options as the answer, please directly output the most appropriate option, do not need to output the explanation.

If a mortgage borrower makes prepayments without penalty to take advantage of falling interest rates, the lender will most likely experience:
Option A:extension risk.
Option B:contraction risk.
Option C:yield maintenance.

Answer: B