阅读短文，从方框中选择适当的词并用其正确的形式填空，使短文意思通顺、完整，其中有两项是多余的。

                              something, swim, class, careful, hour, easy ,think, minute, what,  eye ,  try ,  difficult. 

        It was the first biology class.  The teacher wanted to give a good start to her____   . she wanted to open up her students' ____   to the world of biology . She knew that teaching those young students was not ____  , so she worked hard and ____    to find a good way to teach  them . After ____   a long time , She had an idea . She decided to show the children ____   interesting and give them a lesson at the same time.
She asked her students to watch____  . Then she began . She put a  worn(虫) into a glass of water . the worn ____   around in the water . Then she put a second worn into a glass of alcohol(酒). It was killed after a few ____   .  She asked the students ____  they learned from it . A boy answered , "You showed us that if we drank alcohol, we wouldn't  have worns in our stomaches. "