题目

根据短文内容从A、B、C、D四个选项中选出一个能填入相应空格内的最佳答案。 Is the whale the world’s largest fish? No. It looks like a fish, but it is really a mammal (哺乳动物). Then what’s the world’s largest fish? It’s the whale shark（鲸鲨）. Although the whale shark is our biggest fish and lives in many oceans （海洋）around the world, few people have ever heard of it. Scientists have not been studying whale sharks for very long. Much more needs to be learned about them. A whale shark is sometimes called a “gentle giant (温柔的巨 如图所示为蛙的受精卵发育至囊胚过程中，DNA总量每个细胞体积，所有细胞体积之和、有机物总量的变化趋势（横坐标为发育时间），其中正确的是 [　　] A．①② B．①③ C．②④ D．③④