---The window must have taken you quite a lot of time that day.--- You are right. They ________ for weeks.
A:haven't been cleaned
B:hadn't been cleaned
C:didn't cleaned
D:haven't cleaned
将CO、CO2、H2,HCl,H2O(气)和N2的混合气体依次通过足量的下列物质:①浓硫酸 ②饱和氢氧化钠溶液 ③灼热的氧化铜粉末,充分反应后的剩余气体是( )
下列群体属于真正意义上的集体的是( )
不等式组3x-1>24-2x≥0的解集在数轴上表示为