假如你是Lily，今天下午你们的口语练习的话题是“inventions”。现在，同学们正在构思一篇小作文，题为“What's the most useful invention?”。请你根据下列提示，谈谈你的观点。词数在80词左右，可作适当发挥。

提示：

1）What is the most useful invention in your opinion?

2）Who invented it?

3）Why do you think it's the most useful one?

4）How does this invention change people's life?

5）What's the most useful invention?