问题如下：
Which of the following is not the main monetary policy tool of the central bank?
选项：
A.long-term interest rate
B.reserve requirements
C.open market operations
解释：
A is correct. The main monetary policy tool of central bank contains reserve requirements, open market operation and Policy rate, not the long-term interest rate.
考点：货币政策工具
解析：央行的主要货币政策工具包括准备金率、公开市场操作和政策利率，而不包括长期利率。
我可以这么理解， A 选项是央行的设定的目标， BC 选项是它的手段， 对么?
