rich 1.0 (WASHINGTON)— Federal Reserve Chair Janet Yellen indicated Monday that the U.S. economy is improving but remains defined by so many uncertainties that it's unclear when the Fed should resume raising interest rates. Speaking in Philadelphia, Yellen struck a mainly positive and optimistic tone about the economy. TIME's Top Stories https://audioboom.com/channels/3380207-time-s-top-stories Audioboom https://audioboom.com 480 95 https://audioboom.com/i/22322911/600x600/c 600 600 <iframe width="100%" height="95" src="https://embeds.audioboom.com/posts/4661410/embed?v=202301" style="background-color: transparent; display: block; padding: 0; width: 100%" frameborder="0" allowtransparency="allowtransparency" scrolling="no" title="Audioboom player" allow="autoplay" sandbox="allow-downloads allow-forms allow-popups allow-same-origin allow-scripts allow-storage-access-by-user-activation allow-top-navigation-by-user-activation"></iframe>