_____________________________________________ The White House says the leaders will also discuss additional steps NATO allies must take to address challenges on Europe's eastern and southern periphery, as well as efforts to advance negotiations on the Transatlantic Trade and Investment Partnership. _________________________________________白宫表示在会领导人也可能商讨北约盟国必须采取的措施,以应对欧洲东部和南部边界面临的挑战,以及努力推动跨大西洋贸易及投资伙伴国协议的谈判.