NO.PZ2016031201000028
问题如下：
When interest rates are constant, futures prices are most likely:
选项：
A.
less than forward prices.
B.
equal to forward prices.
C.
greater than forward prices.
解释：
B is correct.
When interest rates are constant, forwards and futures will likely have the same prices. The price differential will vary with the volatility of interest rates. In addition, if futures prices and interest rates are uncorrelated, forward and futures prices will be the same. If futures prices are positively correlated with interest rates, futures contracts are more desirable to holders of long positions than are forwards. This is because rising prices lead to future profits that are reinvested in periods of rising interest rates, and falling prices lead to losses that occur in periods of falling interest rates. If futures prices are negatively correlated with interest rates, futures contracts are less desirable to holders of long positions than are forwards. The more desirable contract will tend to have the higher price.
中文解析：
这里比较的是futures和forward在哪种情况下价格会不一样， 它们的定价公式 其实是一样的，唯一不同的是futures是每日结算。
思考的角度是比较再投资收益的高低，因为futures是每日盯市，每日都会有现金的流入和流出，如果提前拿到现金流，且利率上升，就说明再投资收益上升，此时投资者更希望用futures合约，所以futures就会比forward贵。所以价格上升，long方有收益，即有现金流入，若利率下降，再投资收益下降，投资者就不想提前获得现金流，futures就比forward便宜；若利率保持不变，则forward和futures二者价格相同。
解释是考虑futures和forward的再投资收益，所以是保证金账户里的钱是有收益的么？
