A：滴加石蕊试液显红色的溶液：Fe3+、NH4+、Cl-、I-
B：pH值为1的溶液：Cu2+、Na+、Mg2+、NO3-
C：水电离出来的c(H+)=10－13mol/L的溶液：K+、HCO3-、Br-、Al3+
D：能与铝反应产生H2的溶液：K+、Ba2+、NO3-、Al3+
①鼻毛可阻挡吸入的尘埃 ②鼻黏膜分泌的黏液可使吸入的空气清洁、湿润
③嗅细胞接受气体的刺激 ④鼻黏膜内丰富的毛细血管能温暖吸入的空气
顾维钧回忆他在20世纪初与梅兰芳交往时说到：“有人介绍我和梅兰芳初次见面时，他对我打千（介乎作揖和下跪之间的礼节），其实我不过是外交部的秘书。两年以后我们再次见面时，他向我鞠躬而未打千。以后他从国外演出归来，我们又见面了。从那以后，我们只是握手。”这些变化说明（ ）
People are often killed while c____ the road. Most of them are old people and c____ . Old people are often killed because they are careless. People should look and listen b____ they cross the road. A car, a truck or a bus can't stop very q____ if it is going very fast. It will travel many meters before it s____ . Pedestrian(行人)don't know this. They think that a car can stop right away. It is h____ for a pedestrian to know how fast a car is traveling. The only s____ way to cross the road is to look at b____ ways, right and left. The correct way to cross the road is t____ walk quickly when the traffic l____ turn green.
从刀耕火种到铁犁牛耕，反映了我国古代农业从原始向精耕细作发展的历程。铁犁牛耕的耕作方式出现于（ ）
