hard grades of bitumen

例句：

1. 1. Theteacher gave us hard grades for notturning in our homework on time.
   老师因为我们没有按时交作业而给我们严格的成绩。
2. 2.The exam was a tough one and thestudents had to work hard to earn goodgrades.
   考试很难，学生们必须努力工作才能获得好成绩。
3. 3. Thestudent's hard grades were due to his diligent study habits.
   学生的硬性成绩是由于他勤奋的学习习惯。