介绍一项小发明的短文写作 — 英语填空题
题目
请根据提示完成短文填空，介绍一项小发明（每空一词）。My invention is a robot cleaner. It can help my mother clean the floor. It is small ___ smart. Every morning, it starts to work ___ eight o'clock. My mother is very happy ___ it makes her life easier. I hope my invention will be ___ (有用的) one day.