A：纯碱﹣﹣盐
B：干冰﹣﹣混合物
C：澄清石灰水﹣﹣纯净物
D：洁净的空气﹣﹣纯净物
吨单质铜？（请写出计算过程）
——Would you like to go shopping with me?——I'd love to, _____I can't. I have a lot of homework to do.
