hide a single box of checkbox if a select list value is selected

i have a form with a select list like:

" Choose your category: cat 1 cat 2 cat 3 "

and a checkbox like: " Choose your second category: cat 1 cat 2 cat 3 "

if i select cat 1 from select list, i need to show a checkbox like: choose your second category: cat 2 cat 3

(so i need to hide cat 1 that is the same)

or if i choose cat 2 i must see: choose your second category: cat 1 cat 3

the module hide or show all block and not only 1 value of the block...

can someone help?