Use JavaScript or jQuery to get the values.
For example, if you want to get the value from the firstGroupA using the select's onchange event:
<td><select id="firstGroupA" onchange="jsMethod()" name="firstGroupA" required>
<option value="">Select</option>
<option value="Brazil">Brazil</option>
<option value="Croatia">Croatia</option>
<option value="Mexico">Mexico</option>
<option value="Cameroon">Cameroon</option>
</select></td>
JavaScript:
function jsMethod(){
var firstGroupA = document.getElementById("firstGroupA");
var firstGroupVal = firstGroupA.options[firstGroupA.selectedIndex].value;
// do whatever you want with the value in firstGroupVal
}