A. It's a nice sweater.
B. It's on the line.
C. No, it isn't. It's on the chair.
D. Yes, I have. The coat is nice.
E. No, I haven't. I've got a new pencil.
长江中下游平原开发早期农业经济落后于黄河中下游地区，原因是( )
有一种气体的质量是14.2g，体积是4.48L（标准状况），该气体的摩尔质量是（ ）
