Kranthi, there is no such thing as a ComboBox in HTML.
Please
read this for more information.
Priya, if you want to place the values as separate options, then you need to populate multiple option tags, not a single span or div.
Of course, you will need to add your values and the name of the select element, and the call to your javascript function to the first select element.
For the second select element, you may want to place the values you receive back from your Ajax call into a javascript array, so that you can loop through in a similar fashion.
The key point that I am trying to make, is that if you want each value on its own line, you need to wrap each value in its own <option> element.