第17题: [单项选择]胚胎发展到胎儿的一个重要标志是( ) A. 胎音 B. 骨化 C. 毛发 D. 反射 参考答案:B 答案解析:[解析] 到了第八周末，胚胎开始变得有点“人样”了。骨细胞开始在中心部分再造软骨细胞。骨细胞的出现是在身体的结构分化基本完成的时候，它们的出现，使得已经分化了的结构开始骨化。骨化意味着胚胎发展到了一个
第25题: [单项选择] {$mediaurl}What does the student mean when she says this: A. She does not believe that water is colorless. B. She has difficulty seeing certain colors. C. It is possible to see through water only if it is clear. D. It is interesting to look at things underwater. 参考答案:A 答案解析:[解析] What does the student mean when she says this: "In grade school I was taught that water
