Thirty years ago this month,China's leaders launched an economic revolution.___________the door to free market reforms and foreign trade. A. to open B.opened C.opening D.having opened 答案:C实验室制备并收集CO2,通常有以下操作步骤:①检查装置气密性;②固定装置;③加入大理石;④加入稀盐酸;⑤收集;⑥验满.其中排列顺序正确的是( )
A、①②③④⑤⑥B、②①④③⑤⑥C、①③④②⑤⑥D、②③④①⑤⑥