—What did you do last weekend?
—I ______ to the countryside with my family.
A:go
B:will go
C:am going
D:went
①同质量、不同密度的Cl2和CO ②同温度、同体积的H2和 N2
③同体积、同密度的 C2H4和C3H6两种气体 ④同压强、同体积的N2O 和 CO2两种气体.
薯片等易碎食品宜采用充气袋包装,下列气体中最适宜充入的是( )