JSFiddle - React, Tailwind, and code Playground

HTML

<select name="" id="depth1">
  <option value="">선택</option>
  <option value="a">a</option>
  <option value="b">b</option>
  <option value="c">c</option>
</select>
<select name="" id="depth2">
  <option value="">선택하세요</option>
  <option value="a1" class="depth2_op depth2_a" style="display:none;">a1</option>
  <option value="a2" class="depth2_op depth2_a" style="display:none;">a2</option>
  <option value="b1" class="depth2_op depth2_b" style="display:none;">b1</option>
  <option value="b2" class="depth2_op depth2_b" style="display:none;">b2</option>
  <option value="b3" class="depth2_op depth2_b" style="display:none;">b3</option>
  <option value="c1" class="depth2_op depth2_c" style="display:none;">c1</option>
  <option value="c2" class="depth2_op depth2_c" style="display:none;">c2</option>
</select>

JavaScript

$('#depth1').change(function() {
	$('.depth2_op').hide();
	$('.depth2_' + $(this).val()).show();
  $('#depth2').val('');
})