题目

下列关于细胞分化、衰老、凋亡和癌变的叙述，正确的是（ ）①个体发育过程中细胞的衰老对生物体都是有害的②正常细胞癌变后在体外培养可无限增殖 ③由造血干细胞分化成红细胞的过程是可逆的 ④癌细胞容易在体内转移，与其细胞壁上糖蛋白等物质减少有关 ⑤人胚胎发育过程中尾的消失是细胞凋亡的结果 ⑥原癌基因和抑癌基因的变异是细胞癌变的内因 ⑦低温引起的细胞冻伤和死亡属于细胞坏死 A . 1种 B . 2种 C . 3种 D . 4种 九、课文原句填空（每空0.5分，共5分） 1. Polly found herself ______ _____ _____ a man standing with his hand _________ on her arm. 2. In 1066, the Normans conquered English and _______ ______ ______ the country. 3. Unfortunately, all the people were _______ _______, and _______ was the city.