1차 카테고리에 따라 2차 카테고리가 변하게끔 만들고 싶어요ㅠㅠ 도와주세요.. 채택완료

</p><p> </p><p>                <select name="mb_1" id="reg_mb_1" required class="form-control input-sm nospace"></p><p>                    <option value="">선택하세요</option></p><p><span class="Apple-tab-span" style="white-space:pre">					</span><option value="A" <?php echo get_selected($member['mb_1'],"A");?>>A</option></p><p><span class="Apple-tab-span" style="white-space:pre">					</span><option value="B" <?php echo get_selected($member['mb_1'],"B");?>>B</option></p><p><span class="Apple-tab-span" style="white-space:pre">					</span><option value="C" <?php echo get_selected($member['mb_1'],"C");?>>C</option></p><p><span class="Apple-tab-span" style="white-space:pre">					</span></p><p>                </select></p><p><span class="Apple-tab-span" style="white-space:pre">			</span></p><p><span class="Apple-tab-span" style="white-space:pre">			</span></p><p><span class="Apple-tab-span" style="white-space:pre">	</span></p><p>                <select name="mb_2" id="reg_mb_1" class="form-control input-sm nospace"></p><p>                    <option value="">선택하세요</option></p><p> </p><p><?php if ($member['mb_1']=="A") { ?></p><p><span class="Apple-tab-span" style="white-space:pre">					</span><option value="1" <?php echo get_selected($member['mb_2'],"1");?>>1</option></p><p><span style="font-size: 14.6667px;"> </span></p><p><span style="font-size: 14.6667px;"><? } </span><span style="font-size: 14.6667px; line-height: 22.0001px;">else if </span><span style="font-size: 14.6667px; line-height: 1.5;">($member['mb_1']=="B") {</span><span style="font-size: 14.6667px; line-height: 1.5;"> </span><span style="font-size: 14.6667px; line-height: 1.5;">?></span></p><p><span class="Apple-tab-span" style="white-space:pre">					</span><option value="2" <?php echo get_selected($member['mb_2'],"2");?>>2</option></p><p><span class="Apple-tab-span" style="white-space:pre">					</span><option value="3" <?php echo get_selected($member['mb_2'],"3");?>>3</option></p><p> </p><p><span class="Apple-tab-span" style="white-space:pre">					</span><? } ?></p><p>                </select></p><p><span class="Apple-tab-span" style="white-space:pre">			</span></p><p>