— You ____ have set aside more time to play with our kids.

— I wish I ____, but you know how busy I was.[ ]

A. should, would

B. could, did

C. might, should

D. should, had

已知水的摩尔质量为18g/mol、密度为1.0×10³kg/m³，阿伏伽德罗

常数为6.0×10²³mol^-1，试估算1200ml水所含的水分子数目（计算

结果保留一位有效数字）。