问题补充：
Many people keep small fish _31 pets. They keep them in a tank of water. The tank is made of glass. People can _32 through it. They can see inside the tank and watch the fish.
The fish need room. They mustn’t be crowded. They need _33 to breathe.
34 must be enough water for all fish. So the size of the tank is very important.
In the tank people put small plants 35 are good for fish. They give oxygen to the water. Plants help in other ways, too. They can hide 36 the plants and sleep, lay eggs there.
The fish 37 be kept in water all the time. Some can jump high. So the tank should be covered. This keeps the fish 38 (jump) out.
The fish need food and should be fed every day. But 39 you give them too much food, it is very bad, for the extra food will fall to the bottom and make the water dirty. So the fish should get just enough food and finish 40 in ten minutes. Nothing should be left. 31 as 32 look 33 oxygen 34 There 35 that/which
答案：
(答案→)31 as 32 look 33 oxygen 34 There 35 that/which
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