①NaHSO4 ②NaHCO3 ③Na2CO3 ④Na2SO4.
A:④③②①
B:①②③④
C:③②④①
D:③④②①
分子间存在引力,物体内部的分子必然由于引力的作用而无间隙的团聚在一起是吗?请你用实验或一个现象来说明.
He had hoped to have an opportunity to travel abroad for long. But it was a(n) ______ that he missed it when it came last month.