Many couples with young children and old people prefer fresh grass and natural soil to concrete and cement in a city.

soil 是名词，指"土壤、泥土"，即地球表面由矿物质、有机质、水和空气组成的松散表层，是植物生长的基础。在句中与 concrete（混凝土）和 cement（水泥）形成对比，强调自然与人工材料的区别。