A professor told his students to go into the city slum（贫民窟）to study the life of 200 boys. He asked them to ______reports about each boy's life and future. Every one of the students wrote，"He doesn't have any hope. ”

Twenty-five years ______，another professor read about the earlier study. He told his students to ______ what had happened to the boys. They tried very hard and found that 176 of the boys had become successful ______ doctors，teachers and scientists.

The professor was very ______ and decided to study it further. Luckily，all the men were living near the place and he was able to ask each one，"What made you ______？”Each one answered，“There was a teacher. ”

The teacher was ______ living there，so the professor found her and asked the old woman ______ she had used to pull those boys ______ the slum, and change them into successful people.

The teacher's _______ began to shine and she said with a sweet smile, "It's really very easy. I loved those boys. "