Do you know how to keep fish at home?
   The fish need room. They must not be crowded（拥挤）. Fish need oxygen(氧气). Fish get it from water in the tank. There must be enough water for all fish in the tank. So the size of the tank is important..
   In the tank many people put small plants(植物). They give oxygen to the water. Plants help in other ways, too. Fish can nibble(轻咬)on the plants. They hide in the plants and sleep, lay eggs there.
   Both the plants and fish need light. You can put near a window. It will get light there. But remember: a window may let cold air in. The cold can kill(杀死) your fish. Too hot water can kill your fish, too.
   The fish need food and you should feed them every day. Giving them too much food is bad. It will make the water dirty. However, the fish should get just enough food. They should finish the food in 10 minutes. No extra(多余) is left. When this happens, the amount(数量)of food is right.

阅读材料，回答问题。

材料一： 读图

材料二： 为了巩固统治，西周实行了分封制。周天子把土地和平民、奴隶，分给亲属、功臣等，封他们为诸侯。诸侯必须服从周天子的命令，向天子交纳贡品，平时镇守疆土，战时带兵随从天子作战。

一辆货车箱是一个长方体，它的长是4米，宽是1.5米，高是4米，装满一车沙，卸后沙堆成一个高是5分米的圆锥形，它的底面积是多少平方米？