题目

鱼类在水中可以穿越任何激流，主要是因为它身体上具有可以感知水流方向和速度的 A．侧线    B．鳃       C．胸鳍     D．尾鳍 答案：AThe old scientist devoted most of his time __________ the space science.A. develop B. to developingC. to develop D. developing