问题如下：
Daisy shorts 1800 shares of KIY company's stock on a 30% initial margin and the broker's lending rate is 2.5%. The current price is $65 per share. The broker charges a commission of $0.02 per share on sales but purchases for free. KIY stock pays an annual dividend of $1 per share. One year later, Daisy buys the 1800 shares at a price of $58 per share and close the position.Which of the following is closest to Daisy's rate of return?
选项：
A.24.98%.
B.24.81%
C.32.55%.
解释：
B is correct.
Initial principal = 1800*65*0.3= 35100. The commission on sale( calculating as a part of initial cost)=1800*0.02=36
Remaining principal=1800*65*0.7=81900 ,so the first expense---lending interest=81900*2.5%=2047.5
The second expense---dividend payment=1*1800=1800, and there is no purchase commission.
The return on this investment=1800*65-1800*58-36-2047.5-1800=8716.5
Yield=8716.5/(35100+36)=24.81%
请问一下老师initialprinciple 和remaining principle 是什么意思，我看到老师有回复其他同学“你想借1800，但是自己只有65*1800*30%，所以借了65*1800*70%”，不是很理解为什么实际是借65*1800*70%而不是65*1800*30%，谢谢
