how to create cascading dropdownlist without using postback?

Question

I have taken three  cascading drop down list.

one for country,one for state and the last one for city..

when I select any country from the first dropdown the and then the second will be enabled and will show only that states of a country which i have selected in drop down list.

That is working properly but because of the Auto postback property is true so each time i select country then the page is refreshed then after i select state again the page is refreshed and for city also the page is refreshed.so the page is refreshed thrice.

that i don't want to do.so what should i do to avoid the thrice page refresh??

can I use Ajax cascading drop down list??

How??