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.

The repo margin on a repurchase agreement is most likely to be lower when:
Option A:the underlying collateral is in short supply.
Option B:the maturity of the repurchase agreement is long.
Option C:the credit risk associated with the underlying collateral is high.

Answer: A