题目

The biggest problem with Bob is that he never has got a/ an ___ goal in his life. A. abstract   B. specific   C. delicate   D. aggressive 答案：B 解析: 略氨水是一种化学肥料。打开贮存氨水的容器，就可以闻到一股强烈的氨味。从微观的角度分析，其原因是                                                                          (    )     A．组成氨水的元素种类发生改变    B．氨分子在不断运动     C．氨分子由静止变为运动     D．氨分子的体积变大了