BEIJING (AP) — Global stocks tumbled Friday after tensions over Ukraine mounted and Standard & Poor's cut Russia's credit rating, warning of capital flight and risks to investment due to the crisis. Oil declined but stayed above $101 per barrel amid worries about the possible impact on Russian supplies. S&P said it took the step because the tense situation "could see additional significant outflows of both domestic and foreign capital from the Russian economy." [...] relief was mixed with concern about higher U.S.