A college student stayed up all night studying for his zoology(动物学) test the next day. The following morning, ______ he entered the classroom, he saw ten birds on the desks. Each bird was ______ with a sack(麻布袋) and only the legs were outside.

The teacher told the students that the test would be to watch each pair of bird legs and write down the name and the living habits of each bird.

The student looked at each pair of bird legs. ______ of them looked the same to him. He began to get upset. He stayed up all night studying, but now he had to name birds by their legs. The more he ______ about it, the sadder he got.

He ______ not think of any answers after a long time. He went to the teacher’s desk and said, “What a strange test! ______ could anyone tell differences among birds by their legs? I’m afraid I have to take the exam later. ” ______ these words, the student put his test paper on the desk and walked to the door.

The teacher was______.The class was so big that he didn’t know every student’s ______, so when the student reached the door, the teacher ______ out, “One moment, boy, what’s your name?”

The student pulled up his trouser legs and said, “My dear teacher, can you guess my name by my legs?”