参考答案：A

解析：

If the U.S. Federal Reserve sells government securities for cash, cash is being withdrawn from circulation in the economy. This action will decrease the money supply. A decrease in the money supply will reduce the supply of funds that the banks can loan, which will cause real and nominal interest rates to increase. The increase in real and nominal interest rates will make it more expensive for businesses to finance their capital investments. Therefore, the economy will experience a contraction in business investment, which will also cause aggregate demand to decrease. The decline in aggregate demand will lead to a decline in real GDP, a decrease in the inflation rate, and a decrease in the employment rate.