表示“转折”，除了but，还有这4个词：
1. however
例：This is one possible solution to the problem. However, there are others. 这是该问题的一种可能的解决办法，但还有其他的办法。（牛津词典）
2. nevertheless
例：There was still a long way to go. Nonetheless, some progress had been made. 路还很长，不过已经取得了一些进展。《柯林斯高阶英汉双解学习词典》
