问题如下：
Which of the following statements regarding to repo margin is correct?
选项：
A. Holding other factors constant, the repo margin will be lower when the collateral security is in higher demand.
B. Holding other factors constant, the repo margin will be lower when the repo term is longer.
C. Holding other factors constant, the repo margin will be lower when the credit quality of borrower is lower.
解释：
A is correct.
When repo term is shorter, the repo margin will be lower; When credit quality of borrower is higher, the repo margin will be lower.
虽然排除法选对了，但是能否针对A解释一下。如果有higher demand，不是说明它带来的回报率更高，大家更愿意买么？怎么会是haircut缩小了呢
