题目

All our food comes from the soil (土壤). Some of us eat meat, but animals live on plants. If there were no plants, we should have no animals and meat. So the soil is necessary for life.The top of ground is usually covered with grass or other plants. Plants grow in soil, which has a dark color. This dark soil is humus, dead leaves, dead plants and animal waste make it, but this takes a long time. When the humus has been made, plants can grow well in it.All soil needs food. If we don’t give it any, the plants will be weak. Animals waste is the best food for the soil, but chemical fertilizers能证明细胞渗透吸水原理的最佳实例是（ ）A. 将萎蔫的青菜放入清水中会变得硬挺B. 将根尖细胞放人清水中会吸水C. 将土豆块放入盐水中会失水变软D. 细胞的呼吸作用