SRAS回到原来是哪个理论导致的?为什么不会保持变化

问题如下：

Following a sharp increase in the price of energy, the overall price level is most likely to rise in the short run:

选项：

A.and remain elevated indefinitely unless the central bank tightens. B.but be unchanged in the long run unless the money supply is increased. C.and continue to rise until all prices have increased by the same proportion.

解释：

An increase in energy prices will shift the short-run aggregate supply curve (SRAS) to the left, reducing output and increasing prices. If there is no change in the aggregate demand curve, in particular if the central bank does not expand the money supply, slack in the economy will put downward pressure on input prices, shifting the SRAS back to its original position. In the long run, the price level will be unchanged.

中文解析：

能源价格的上涨将使短期总供给曲线(SRAS)向左移动，从而减少产出并提高价格。如果总需求曲线没有变化，特别是如果央行不扩大货币供给，那么经济的疲软就会给投入价格带来下行压力，使SRAS回到原来的位置。从长远来看，价格水平将保持不变。