题目

It was the last day of the final examination(考试)in a college. On the steps of building, a group of engineering students were waiting for the last exam. On their faces was confidence(自信). They knew the exam would be easy. The professor(教授) had said they could bring any books or notes during the test. Right after they came into the classroom. The professor handed out the papers. There were only five questions on it. Three hours passed. Then the professor began to collect the papers. The students no longer looked confident. On their faces was nervous expression. The professor watched 关于“蜻蜓点水”现象的正确解释为（   ） A．蜻蜓在飞翔中饮水的现象                        B．蜻蜓通过身体触及水作标记 C．雌性蜻蜓的产卵行为                            D．雄性蜻蜓的求偶行为