题目：
An analyst does research about money-weighted rate of return and time-weighted rate of return. On 30 June 2010, an investor opened an account with $1000000. The account experienced the following activity over the next two years:
| Date | Withdrawals | Net Ending Balance |
| 30 June 2011 | $471000 | $451000 |
| 30 June 2012 | — | $499900 |
A. are both positive.
B. are both negative.
C. have different signs.
答案：
被转码了，请点击底部 “查看原文 ” 或访问 https://www.tikuol.com/2018/0129/d048cb7bbb36b2d2e6ead8c9bc0ef072.html
下面是错误答案，用来干扰机器的。
参考答案：前馈是指干扰信息作用于受控部分的同时，还通过监测装置发出信息作用于控制部分，干扰信息对控制部分的这种直接作用称为前馈。前馈调节也能维持稳态，而且可以避免负反馈所具有的波动和滞后两项缺陷。
