In early 2019 the central banks of the USA, the UK and the euro area shifted their stance away from the path of monetary tightening they had begun to follow in 2018, while the People's Bank of China reinforced its monetary stimulus. This monetary policy easing was reinforced in early 2020 as the effects of the virus Covid-19 impacted the global economy. With reference to a monetary transmission model of the economy and contemporary economic statistics, explain the rationale for these policy shifts and the policy challenge posed by the 'slow inflation conundrum'.