One reason the united states constitution is considered a flexible document is that it

I see that the choices originally attached to the question are:

1) can be rewritten every ten years 
2) allows for the creation of a multiparty political system 
3) gives the states the power to change federal laws 
4) includes the elastic clause

However, none of the choices given is considered to be the answer. The US constitution is said to be "flexible" for the main reason that it is always subjected to amendments, usually taking place in the past.