I have a form and I want to have two select boxes so that in one of them certain options would show/hide based on the current value of another select box.

e.g 

```
Select box X Options :
A
B

Select box Y Options :

1 // shows only when A is selected in Select box X
2 // A
3 // A
4 // shows only when B is selected in Select box X
5 // B
6 // B

```

Help please.