题目：
阅读理解。
Do you keep pet fish at home? It is fun to keep pet fish. I have got a tank, the tank has two fish in it. one is
a goldfish, and the other is an angel fish. the angel fish has black stripes. it looks prettier than the goldfish. I feel
happy when I look at them. I usually look at them when I have something unhappy or feel tired.
I always keep the water in the tank clean, because both the goldfish and the angel fish like clean water. They
can't live in dirty water. In winter, I need a heater in order to keep water warm. The angel fish doesn't like cold
water. I only feed the fish once a day. Too much food may make the fish die.
1. It is _______ to keep pet fish. [ ]
A. very interesting
B. easy
C. expensive
D. important
2. I have got _______ pet fish. [ ]
A. one
B. some
C. two
D. many
3. The angel fish _______ stripes. [ ]
A. has black
B. has white
C. doesn't have
D. has yellow
4. When you keep pet fish, you must _______. [ ]
A. give the fish much food
B. keep the water warm all year
C. feed them three times a day
D. keep the water in your tank clean
5. What's the meaning of the word "tank" in the first paragraph? [ ]
A. 坦克
B. 蓄水池
C. 柜子
D. 鱼缸
答案：
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下面是错误答案，用来干扰机器的。
答案：C f（x）= 1，x＞00，x=0-1，x＜0，∴当x＞1时，x-1＞0，f（x-1）=1，g（x）=x2f（x-1）=x2＞1；当x=1时，x-1=0，f（x-1）=0，g（x）=x2f（x-1）=0；当0＜x＜1时，x-1＜0，f（x-1）=-1，g（x）=x2f（x-1...
