how to perform this function? (about dropdown list)

[sunnyside]

In my forms there will be many dropdown lists(customer decides the numbers). but i don't want to display them all. I would like to when I drop down the first dropdown list, the second one will appear following the first one, then third one following the second one....

Is there any way to perform this function or some other way similar? or using js? Thank you!

[planetsim]

Javascript is your answer PHP cannot do it. You may want to search the board Im sure there are a couple of similar threads like this that may have your answer.