根据短文内容和首字母的提示，把所缺单词填写在短文后面的横线上。

Robot s  70  are not just trying to make robots look like people. For example, there are already robots w  71   in factories. These robots look more like huge arms. They do simple jobs over and over again. People would not like to do such jobs and would get bored. But robots will never get bored. In the future, there will be more robots e  72   , and humans will have l73        work to do. New robots will have many different shapes. Some will look like humans, and others might look like snakes. After an earthquake, a snake robot could help look for people under b  74  . That may not seem possible now, but computers, space rockets and even electric toothbrushes seemed i   75    a hundred years ago. We never know what will happen in the future.

下列器官属于并联结构的是（）。

A.脑干

B.脊髓

C.肺

D.小肠

E.食道