第二节：语法和词汇知识（共15小题，每小题1分，共15分）
从每小题所给A、B、C、D四个选项中，选出可以填入空白处的最佳选项。
Our teachers are really ______. They often work in their office far into the night.
A. open-minded   B. hard-working    C. self-confident    D. warm-hearted