题目

It was in the Ming Dynasty __________ the Great Wall was rebuilt to keep out northern tribes _________ threatened the Chinese heartland.    A．that; that              B．that; where         C．when; that         D．when; when 答案：A下列图象中有关量的变化趋势与对应叙述关系正确的是（ ）A．向氢氧化钠和碳酸钠的混合溶液中滴加盐酸至过量B．向一定质量的稀硫酸中滴加水C．向接近饱和的硝酸钾溶液中加入硝酸钾晶体D．加热一定质量的高锰酸钾固体