理论换算法适合定量包装的商品、非定量包装的商品和附有码单的商品。
参考答案：错
— ____ sweep the classroom yesterday？
—I was playing tennis with my friend．
A．Why not
B．Why didn't
C．Why don't
D．Why didn't you
用“
”、“
”分别表示不同元素的原子，下列由分子构成的物质中属于化合物的（ ）
A．
B．
C．
D．
