Concat itself is a an extension method implemented as such.
代码中的Concat是一个扩展方法(extension method)，其实现如下。
Education (at least high school) is a an essential foundation for every single person today.
今天教育(至少高中教育)对于每个人是十分重要的基础。
In front of me lay the whole valley like a an untouched paradise on earth.
在我面前展现着整个山谷，像是一个世外桃源。
After 2 days of work on Task a, an emergency occurs.
处理任务a的两天之后，紧急事件发生了。
这里有个物体。
A: An agreement has been established after tough negotiation.
A：经过艰难的谈判后，终于达成共识了。
I am surprised that you should have been fooled by such a (an) simple trick.
我很吃惊你竟被这样简单的把戏给愚弄了。
A: An octopus has eight tentacles!
一只章鱼有八只脚耶！
A: An octopus has eight tentacles!
一只章鱼有八只脚耶！
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