问题如下：
Which of the following refers to the difference between the market value of the security used as collateral and the value of the loan?
选项：
A. Repo yield.
B. Repo margin.
C. Repo rate.
解释：
B is correct.
The repo margin or haircut is the difference between the market value of the security used as collateral and the value of the loan. The repo rate is the interest rate on a repurchase agreement.
老师问下 repo rate 和repo margain的区别是什么呢