回复：Money supply and inflation

Fed Open Market Operations buy/sell gov bonds from/to commercial banks to maintain the short term interest rate target, therefore add/drain the monetary base. OMO buying is also know as "pumping money into the economy"(strictly speaking this is not "printing money", which stopped long before you were born).

Fed will pump if there is pressure for interest rate to rise(too many people borrowing). It might be viewed as effect instead of cause.