(FILES) This file photo taken on March 12, 2020 shows the headquarters of the European Central Bank (ECB) in Frankfurt am Main, western Germany. - Germany's Constitutional Court ruled on May 5, 2020 that the European Central Bank must clarify a key bond-buying scheme to support the eurozone economy is "proportionate" or else Germany's Bundesbank central bank may no longer participate. (Photo by Daniel ROLAND / AFP)