Miss Richards was a teacher at a school for boys and girls. She1 Chemistry and Physics from the lowest to the highest classes in the2 . Sometimes the new classes learned 3 , but sometimes they were very 4 , and then Miss Richards had to5 things many times.
One year, the first class had been studying Chemistry for several 6 when Miss Richards suddenly asked, "What is water? Who knows?7 up!"
There was silence for a few seconds，and Miss Richards felt sad，but then one boy 8 his hand.
"Yes，Dick?" said Miss Richards encouragingly. He was not one of the brightest children in the class，so she was9 that he could answer.
"Water is a liquid which has no10 until you wash your hands in it，Miss. Then it turns black," the boy replied with great confidence.
