根据句子意思，用所给单词的适当形式填空。未提供单词的根据上下文填入适当的词。

Thomas Edison was a famous American scientist. When he was  child, he liked to find out  things worked. In school he asked his teacher a lot of questions which had nothing  (do) with his lessons. So his teacher thought he was not worth  (teach).Soon he got very  (interest) in science.

Once he thought out a good idea to make the room bright  (save) his mother's eyes.  he was 15, he saved a boy and he learned to send messages  railway telegraph from the boy's father. Ever  then, he never  (stop) searching for new and better ways to do things.