You have ____ ____ ____; I think you'd better lose weight.
将下列物质前的序号填入适当的空格中:
①稀盐酸 ②消石灰 ③碳酸钙 ④氢氧化钠 ⑤氢气 ⑥硝酸钾
胎儿与母体进行物质交换的结构是( )