单项选择题

Professor Tom was going to meet his students on the next day, so he wrote some words on the blackboard which read as follows: " Professor Tom will meet the class tomorrow. " A student, seeing his chance to show his sense of humor after reading the notice, walked up and erased the "c" in the word "class". The professor noticing the laughter, wheeled around, walked back, looked at the student, then at the notice with the erased "c", calmly walked up and erased the "I" in " lass", looked at the frightened student and went on his way. All "asses(蠢驴)" were embarrassed(尴尬的).
A student erased a letter to correct Professor Tom’s mistake.