书中有论述图表：The downward-sloping Aggregate Demand Curve 解释到:

so when price rise from P1 to P2 (upwards),the real money supply (defined as the nominal money supply divided by the price level )must fall . As the real money supply contracts, money becomes relatively scarce or "tight ". Interest rates rise from r1 to r2 (upwards ), and credit becomes more difficult to obtain ;tight money causes a decline in investment and consumption ,thus in output from Y2 to Y2 (decrease).For instance , if the nations money supply is constant at $1000billion , and the consumer price index rise from 100 to 200 , the real money supply falls from $1000billion to 500 billion

condition:other things are constant

问题：1.银行利率是否在无外力条件下自然上升？

２．开信用证一般需要什么条件？

３． consumer price index　一般如何计算？

ＰＬＵＳ：　因为只学了一点西方经济学的微观部分，所以对宏观经济学了解浅薄望大侠指点！不甚感谢！