Link between two drop down lists

Hi all,

I ve created a form in which there are two drop down lists.

Let's one drop down list contains three items A,B,C

and another drop down contains three items Apple,Banana and Cherry.

So,my query is how to create a relation between these two dropdown lists,so that if I will select 'A' from the 1st drop down list, Apple will be selected automatically from the 2nd drop down list.

Thanks,

Debadas