根据首字母以及括号里的提示补全单词
Gina is a s_______ girl(clever)
I will live in an a______ alone.(a number of rooms in a building to live in)
David wants to be ana_______ when he grows up.(a man who travels in
space)
In big cities,air p______ is very serious.(the state of being polluted)
R_______ can do many things for human beings in the future.(a kind of machine which can do something like people)