第19题: [单项选择]The main idea of the passage is ______. A. the development of sonar technology B. how to avoid ship and whale collision C. the hot spots for whale collision D. the giant creature of the sea 参考答案:B 答案解析:本文主要讲了通过sonar technology避免船只与鲸鱼的碰撞以保护鲸鱼的安全,选项B符合文意。