Я так понял, это надо?
<script>
function loadCar(v){
alert(v);
}
</script>
<form>
<select id="f_MarkaModel" name="f_MarkaModel" onchange="loadCar(this.value)">
<option value="kill">kill</option>
<option value="all">all</option>
<option value="humans">humans</option>
</select>
</form>