I have a select 3 dynamic select option on the last select option there is always 1 option only

<select class="wpce-field-term" id="wpce-3" data-level="3" data-required="no" data-required-message="" data-type="term">
    <option value="">PCD</option>
    <option value="15437">5x108</option>
</select>

but it is dynamic.

i want to always auto select the first option so i use this

$("#wpce-3 option:nth(1)").attr("selected", "selected");

but the problem is that it is dynamic and the third option is not yet available until select option 1 > select option 2 are selected