The global economic slowdown _______ millions of migrant workers jobless has caused thousands of firms to close down this year.A. left B. to leave C. leaving D. to be leaving 答案:C11.沪昆高速铁路是我国“四纵四横”的快速客运通道之一,已于2016年全线通车,观察混昆高铁客运专线图,沪昆高铁修建过程中不可能遇到的障碍是( )A.喀斯特地貌,地形崎岖B.穿越雪峰山脉,坡度大C.多滑坡、泥石流等自然灾害D.冰川广布,冻土深厚