斩假石空鼓，产生原因是：中层表面______，造成面层粘结不牢；施工时______，产生干缩不均或脱水快而干缩空鼓。
参考答案：未划毛；浇水过多、不足或不匀
把一元二次方程x（x+4）=12化为一般形式是______，二项系数是______，一次项系数是______，常数项为______．
Great changes _____ in our country recently.[ ]
A. have happened
B. happened
C. have been happened
D. were happened
