C＃无法将欧元符号打印到文件中（使用Excel打开时）

I have a problem with a get method into a web api controller. This method returns a HttpResponseMessage object which has a HttpContent with a csv file, which contains euro symbols. When the method returns the file, the euro symbol isn't printed. The code of the method is the following:I have a problem with a get method into a web a