Wu Yifan had dream last night.
A:an interesting
B:a interesting
C:an interest
Lei Ting is studying very hard. ____ ____ ____, she got high score in this exam.
在描述物体运动时,我们引进了一些物理量和研究这些物理量的方法.下列哪种方法是研究平均速度这个概念( )
7197的分子分母减去同一数之后为23,则减去的数是____ .