题干
When will the film begin?
A：At 6:30 p.m.
B：At 7:00 p.m.
C：At 7:30 p.m.
答案(点此获取答案解析）
B
When will the film begin?
A：At 6:30 p.m.
B：At 7:00 p.m.
C：At 7:30 p.m.
N2O4，所得混合气体中NO2的体积百分含量为40%，此时，混合气体的平均分子量为
