智课网TOEFL备考资料托福写作TPO10综合写作详细解析 阿拉斯加州的海獭数量在减少?是环境污染?还是天敌捕食? 阅读材料： The sea otter is a small mammal that lives in waters along the western coast of North America from California to Alaska. When some sea otter populations off the Alaskan coast started rapidly declining a few years ago, it caused much concern because sea otters play an important ecological role in the coastal ecosystem. Experts started investigating the c
