Hi,
I assume that you looking to display the categories in four levels in different dropdown means while selecting car in the fist box, the sub-categories of the cars should be displayed in the second box. While selecting used cars in the second dropdown, the subcategories of the used cars should displayed in the third dropdown...
If so sorry this feature is currently not available in Jom Classifieds. Currently the second dropdown will contain all the sub categories.
Thanks