i don't know how to see the values i select in a list form Options

[mobutu_LM2006]

I want to see the values wich i select in a list form.

The code is :
"
<select name="categoria_insert" size="3" id="categoria_insert">
<option>A</option>
<option>B</option>
<option>C</option>
<option>D</option>
<option>E</option>
</select>
"

If i select options 'A' and 'D', for example, the value posted in $_POST['categoria_insert'] when i push the submit button is only 'D', not 'A' and 'D'.

Help me please.
Thank you.