题目

World Expo 2010 Shanghai China, a grand-scale global event, has ______ the significant theme “Better City, Better Life.” A. abandoned       B. adopted            C. advocated       D. adapted 答案：B只用空气鉴别甲烷、乙烯、乙炔三种气体，可将三种气体分别____________________ ____________观察________________________________和____________________________。