A student went to college(大学) after passing all his school e

A student went to college(大学) after passing all his school examinations.There he put his name down for world geography,__1___after the first day,he did not go to__2__ any more.The teacher noticed that this student was __3__ absent (缺课) and thought that he had changed to ___4__ class.He was very surprised when he saw the boy's name on the list(名单) of students__who___ wanted to take the geography examination ___at the end of the year.The teacher had prepared a difficult examination paper,which covered （覆盖）__everything___he had taught,and he was eager(急切) to see __how__ this student answered the questions.He expected （期望）that his answer would be very ___bad; but when he examined his paper carefully,he found only one small mistake in them.___10___this surprised him very much,he went through the paper ___twice,but was still not able to find __12___ one mistake,so he sent for the student to question him about his work..When the student had ___13___ the room,the teacher said to him,"I know that you came to my class only once on the first day and that you have been absent from all the others.Yet I have found only one small mistake in your paper.What is that?" "Oh,I'm sorry about that mistake,sir,"answered the student."After the examination,I realized ___14___ I ought to have written.I would not have made that mistake if I had not been confused(弄糊涂) by your ___15____lecture."
The teacher had prepared a difficult examination paper这句话中的difficult我不知道为什么不是ordinary从哪可以看出是填这个词的