第1题: [单项选择]多种鱼类背部发黑,腹部发白,其原因是: A. 长期进化形成的保护色 B. 背部比腹部接受光线多,导致色素沉淀 C. 背部比腹部黏膜厚,吸收光线多 D. 背部鱼鳞多,吸收光线多 参考答案:A 答案解析:[解析] 多数鱼类背部发黑、腹部发白,此为一种长期进化而形成的保护色,因为有了这种保护色,无论从上面或下面观察,鱼类保护色使其易与自然环境混成一体,可以轻而易举地躲避水鸟或肉食性鱼类的捕食。
A. a car bomb exploded in Moscow B. two trains collided at a train station C. a bomb exploded in Moscow D. an airplane crashed in Moscow 参考答案:C 答案解析:[听力原文]26-28 Russia: At least nine people were injured when a small bomb exploded at a busy un