JSFiddle - React, Tailwind, and code Playground
HTML
<form class="form-inline left" method="POST">
<div class="form-group">
<label for="listar">Listar por</label>
<select id="filtro" name="filtro" class="form-control" onchange="this.form.submit()">
<option value="">Escolha algo:</option>
<option value="professor">Professor</option>
<option value="assunto">Assunto</option>
</select>
</div>
</form>