阅读理解。
Long， long ago there were a lot of donkeys. The donkeys worked hard every day. They had no time to play or to relax， but they never felt appreciated(赏识)for the work they did.
One day two donkeys got bored. They wanted to live a comfortable life， so the donkeys went to see a wise old man. They told him their problem. The wise old man agreed that they worked too hard， and he wanted to help the donkeys. “I have an idea，” he said.
“What is your idea?” asked the donkeys.
“I will paint you and no one will know you are donkeys，” said the man.
The man went off to find some paint and he returned in just a few minutes. He had two pots of paints. One pot was filled with white paint， and the other black paint.
The old man first painted them white， and then painted black stripes over the white paint. When he finished， the donkeys did not look like donkeys at all. “You no longer look like donkeys，” the old man said. “Everyone will be fooled. I will call you something else， Zebras.”
The zebras went to a field to eat grass. Now they did not have to work.
Soon， other donkeys saw the zebras. They asked the zebras where they came from. When the zebras told the donkeys their secret， the donkeys all rushed to see the old man.
“Please make us into zebras， too.” They pleaded. So the wise old man painted more donkeys. As he did， more and more donkeys came.
The old man could not paint fast enough. Soon the donkeys became impatient. They began to kick about， and they knocked over the paint pots.
There was no more paint. The painted donkeys ran off to become zebras. The unpainted donkeys， because of their impatience， had to return to work.
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相切，则直线
的倾斜角为 （ ）
