题目

I soon found that the work I was doing had already been done by someone else.________，I was wasting my time.     A．In other words       B．In a word         C．First of all      D．Believe it or not 答案：A公安干警在缉毒行动中，训练有素的缉毒犬屡建奇功，它可以嗅出毒品的原因是（   ） A．分子在不断运动         B．分子是可分的     C．分子体积极小           D．分子间有空隙