问题如下：
As the price level declines along the aggregate demand curve, the interest rate is most likely to:
选项：
A.decline.
B.increase.
C.remain unchanged.
解释：
A is correct.
A decrease in the price level increases the real money supply and shifts the LM curve to the right. Since the IS curve is downward sloping, the IS and LM curves will intersect at a higher level of income and a lower interest rate.
考点：AD曲线
解析：当价格水平下降时，表明真实货币供给增加，LM曲线发生向右平移。与IS曲线交于更低的位置，这个位置对应的利率水平就更小，所以A选项正确。
老师，这题用AD的画图思维直接可得P下降，Y上升，然后推断出来R是下降的。但是如果用答案中的LM曲线思维，因为LM图是正相关的upward sloping， Y上升，r就会上升，不明白为什么要用LM 曲线去解题？而且这两个r 一个上升一个下降，怎么理解？谢谢
