无土栽培是现代农业的一项新技术，其营养液是多种化合物的混合溶液，含有植物生长所需的营养元素．某种植物进行无土栽培时，需含氮、钾等元素的中性或弱酸性营养液，下列能用来配制营养液的一组化合物是（ ）
A：KCl、（NH4）2SO4，NaOH
B：NH4Cl、K2SO4
C：KNO3，H2SO4
D：K2CO3，CaCl2
根据短文理解，选择正确答案。
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北京到广州的直线距离是1800千米，在地图上两地距离是6厘米，此图的比例尺是（ ）
