问题如下：
When the authority has cut nominal interest rate to zero but failed to simulate the economy, it may refer to:
选项：
A.targeting reserve levels is more important than targeting inflation rates.
B.liquidity trap.
C.the effectiveness of monetary policy.
解释：
B is correct.
The setting in which an official interest rate reaches to zero without stimulating the economy suggests that there are limits to monetary policy. It is at this point that the economic conditions for a liquidity trap arise.
考点：liquidity trap.
targeting reserve 并不会影响利率，它并不比 targeting inflation重要， 所以A选项不正确。
当利率水平降低到0时，还无法刺激经济发展（货币政策失效），那么经济就进入了流动性陷阱的状态，所以B选项正确。
C选项liquidity trap说的是货币政策的无效性，所以C选项不正确。
解释里的c是不是搞错了，liquidity trap就是流动性陷阱
