dropdown boxes

I am having trouble with creating two dropdown boxes that rely on each other. I want to show a list of options for the first box and then only show related items in the next box. For example, fruit or vegetable for the first box and apple, banana, carrot for the second box. When fruit is selected apple and banana should appear in the second box and if vegetable is slected the carrot should be the option in the second.
 
Any help would be great!
 
Thanks in advance!
umh3