阅读理解。
Once upon a time, there were two thieves who wanted to steal some sheep .which were fed by a
farmer. They had watched the sheep for a long time. And they knew that there were twenty-eight sheep
in the farmer's yard.
In a deep night, they came to the outside of the farmer's yard and got ready to steal all the sheep. But
they found that the gate was locked inside, and they couldn't open it. Finally, they came up with a good
idea. They dug a big hole in the wall so that one of the thieves was able to go into the yard and pass the
sheep out one by one to the other. In order to stop the sheep from running away, the thief outside must
cut off its head quickly with a sharp knife while the thief inside was passing a sheep out of the hole.
They started to work like that and the work was going well. "One, two, three...,"they both counted
the numbers silently, "...twenty-six, twenty-seven..." However, the thief inside stopped counting. "Where
is the twenty-eighth sheep?" he thought. "Did I make a mistake?" So he stretched （伸) his head out of
the hole to ask the other thief. However, the thief outside thought it must be the twenty-eighth sheep's
head. He didn't think about anything and cut off the head at once.
The two thieves never knew that one of the sheep would have a baby sheep and it had bean sent to
the vet by the owner before they came that night.
根据短文内容，回答下列问题。
1. What did the two thieves want to do?
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2. How many sheep were there in the farmer's yard?
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3. Why did the thief outside cut off the sheep's head quickly?
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4. Did the thief outside cut off the head of the twenty-eighth sheep?
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5. Where was the twenty-eighth sheep?
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试根据上述资料填空。