[Octane]

<form method="get">
	<select name="ab" onchange="if (this.selectedIndex) this.form.submit()">
		<option value="-1">--</option>
		<option value="1">option 1</option> 
		<option value="2">option 2</option>
		<option value="3">option 3</option>
	</select>
	<input type="submit" />
</form>