Thinking about how we might be in 10,20 travel travelled travelling

Câu hỏi :

Thinking about how we might be (1)............... in 10,20 or even 500 years is enough to make the mind melt. Will we still even be (2)…… planes (perhaps we (3) ............... flying our cars from Seattle to Paris)? What if in 100 years we could (4)............... straight to our next holiday destination?