<select name="f[978][]">
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
<option value="5">5</option>
<option value="6">6</option>
</select>
<select name="f[978][]">
<option value="?">1..3</option>
<option value="?">4..6</option>
</select>
Array(f[978][1]=4,f[978][2]=5,f[978][3]=6)
?