____     ____     ____   

人体缺乏必需的元素易患疾病，下列说法正确的是（　　）

​

周长是____cm ，面积是____ $c{m}^2$ ．

    There will be many changes in our life in the future. We will____ flying cars to work. We will travel to ____ . Maybe we will ____ live in space. Students won't ____  schoolbags to go to school any more. They will learn on ____ at home. And there will be robots in our home. The robots will help us do all the housework. Life will be great at that time.