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. (   )16. A tank near the window may NOT be good for pet fish because________. A. no air can get in through the window   B. pet fish will jump out of the window C. plants in the tank will grow too big     D. cold air may make the water too cold (   )17.________is very important to pet fish. A.  Water    B.  Sunlight   C. The size of the tank      D. All the above (   )18. Which of the following may cause（导致） pet fish to die? A. Too little room for fish.             B. The plants in the tank. C. The light through the window.        D. A lot of water in the tank. (   )19. The word 'this' in the last paragraph refers to(指的是)________. A. giving pet fish too much food           B. giving pet fish too little food C. giving pet fish the right amount of food    D. giving pet fish enough water (   )20. This passage mainly talks about______________. A.why fish must be put in a glass tank B. how people should keep their pet fish C. what kind of plants is good for pet fish D. how much food should we give to pet fish