i want list box1 selected index result appear in listbox2 in php

i want list box1 selected index result appear in listbox2 in php

that means when i select country INDIA then all its state appear in second
list box in php like
code given below
first for country
<select name="select3">
<option value="0">-----select-----</option>
<option value="1">India</option>
<option value="2">USA</option>
</select>
and Second List Box For State for that selected Country
<select name="select3">
<option value="0">-----select-----</option>
<option value="1">Maharastra</option>
<option value="2">Kolkata</option>
<option value="3">New York</option>
<option value="4">Washignton</option>
</select>
So When we select India in Listbox1 then related state for india appear in
listbox2 i.e maharastra & Kolkata
so How Code for These Problem