邦德原理认为，粉碎物料所需要的有效功与生成的颗粒的直径的平方根成（）
参考答案：反比
Our town________poor in the past,but great changes________in the town in the past three years. [ ]
A. was; had taken place
B. was; have taken place
C. has been; had taken place
D. has been; have taken place
如图所示，试管内盛水，U型管盛的是红色墨水，当向试管中溶解下列_______时，U型管的b端墨水上升，而a端墨水下降．
①生石灰②熟石灰③浓硫酸④氢氧化钠⑤食盐．
A、①③④
B、②③④
C、①③④⑤
D、①②③④
