题目内容：
阅读下面短文，掌握其大意，然后从21-30各题所给的ABC和D项中，选出最佳选项，并填写在答题卡上将该选项涂黑。 Every country has its own culture.
Even though each country uses doors. .Doors many have__21___functions and purposes which lead to ___22__differences.
When I first came to America, I noticed that a public building had two different__23___ and they had distinct functions. You have to push the door with the word “PUSH” to go out of the building and to pull the door with the word “PULL” to____24_____the building. This was new to me, because we use the ____25____door in south Korea. For quite a few times I failed to go out of a shopping centre and was embarrassed.
The way of using school bus doors was also ____26____to me .I used to take the school bus to classes. The school decided that when the driver opened both the front and back doors,27_____who were getting off the bus should get off first , and students who were getting on should get on __28__. In south Korea, we do not need to wait for people to get off. One morning, I hurried to the bus ,and when the bus doors opened, I___29____tried to get on the school bus through the front door. All the students around looked at me, I was totally_____30____,and my face went red. A．different
B．important
C．practical
D．unusual
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