Have you ever seen a horse with toes? Millions of years ago, horses had many toes. They had four toes on each front foot. They had three toes on each back foot. The horses were no bigger than the cats. These small horses lived in the forest. The toes helped the horses run on the soft, wet ground.

    At first, it was very hot in the forest. But the weather changed. It became very cold. Many trees could not live in cold weather. The trees died and fell. Open fields took the place of forests. The sun made the ground dry and hard.

    Horses began to change, too. They began to get bigger. This took a long time. On the dry, hard land, horses needed only their middle toes for running. Their middle toes became hard. After a long time, horses had only one hard toe on each foot. Now we call this hard toe a hoof(蹄子).

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血液是一种宝贵资源。但由于血源匮乏、运输和保存等困难，迫使科学家们一直在寻求有效的血液代用品——人造血液。

1966年，美国医学博士Clark在进行实验时，由于一时疏忽，一只老鼠意外地掉进了盛有氟碳化合物溶液的容器中，3小时后Clark才察觉这个不速之客，将其捞出，结果本应淹死的老鼠仍还活着。这是什么缘故呢?经过研究，Clark发现氟碳溶液含氧量极高，是水的20倍。比血液含氧量高2倍多。Clark意识到氟碳溶液可能是人造血液的理想材料。

1968年美国哈佛大学教授盖耶从一只麻醉老鼠身上抽去了90%的血液，代之以一种白色氟碳乳液，麻醉老鼠不仅苏醒且存活了8小时。

1978年日本医生内藤良一用全氟碳奈烷和全氟碳三丙胺的混合物做原料，经乳化制得一种氟碳乳液。在经大量动物实验后，给自己身上注入了50mL，结果没有不良反应。这是人造血液成功运用于临床的第一个创举。1979年，我国也研制成这种氟碳人造血。

1979年日本医科大学将人造血液用于临床，效果良好，从此人造血液被医学界正式认可。人造血液不受血型限制，且易于运输，无毒无菌。但一般人造血液只有运输氧的单一功能，尚无代替“全血”功能的代用品。

依据血红蛋白的特性，科学家也在思考可否将血红蛋白直接注入人体发挥作用。但在早期实验中，将游离的血红蛋白注入患者体内，游离的血红蛋白会发生降解且降解速度很快，导致肾脏严重损伤，并且产生自由基，破坏心脏和其他器官，最终导致患者死亡。必须对其进行改良后才能注入人体。目前，经化学修饰后的血红蛋白产品已进入临床试验阶段，并取得了令人瞩目的成果。

图片共同反映了我国的（   ）

下列运动的物体中，运动状态没发生改变的是（　　）