Actuliser une partie de formulaire

		<form id ="tache" method="post" action="" name="insription">
		<fieldset>
		<legend><b> créer le BRQ</b></legend>
			<b>site</b><br/>
				<input type="text" name="site" maxlength="50" /><br/>
			<b>lieu :</b><br/>
				<input type="text" name="lieu" maxlength="10"/><br/>
			<b>heure :</b><br/>
				<input type="time" name="heure" maxlength="10"/><br/>
			<b>date :</b><br/>
				<input type="date" name="date" maxlength="10"/><br/>
				<b>degat corporel</b><br/>
				<textarea type="text" name="degat_c" maxlength="10"></textarea><br/>
<b>degat materiel</b><br/>
<textarea type="text" name="degat_m" maxlength="10"></textarea><br/>
<b>degat envirennemental</b><br/>
<textarea type="text" name="degat_e" maxlength="10"></textarea><br/>
<b>fatalite_E :</b><br/>
				<input type="text" name="fat_E" maxlength="10"/><br/>
<b>fatalite_N</b><br/>
				<input type="text" name="fat_N" maxlength="10"/><br/>
<b>causes :</b><br/>
				<input type="text" name="causes" /><br/>
<b>circonstances :</b><br/>
				<input type="text" name="circ" maxlength="25"/><br/>
<b>jours perdus:</b><br/>
				<input type="text" name="jours_P" maxlength="10"/><br/>
			
	<?php
	include("connexion.php");	
		$req=" select * from  tache  ";
		$req=$connexion->query($req);
		$tache1=-1;		
		if(isset($_POST['tache']))
		$tache1=$_POST['tache'];
		else $tache1=-1;
		echo"<td><select name='tache' id='tache' onchange=\"document.forms['tache'].submit();\">";
		 while($l=$req->fetch())
		  {
		    echo"<option value='".$l['code_tache']."' ";
			if($tache1==$l['code_tache'])echo "selected='selected'";
			echo">".$l['nom_T']."</option>";
		  }
		echo "</select></td></tr>";
		//afficher les risque de la tache selectionner 
			echo"<tr><td>selectionner le risque :</td>";
		$q=" select * from  evaluation e,risque r where e.code_risque=r.code_risque and e.code_tache='$tache1'"  ;
		$q=$connexion->query($q);
		$risque1=-1;		
		if(isset($_POST['risque']))
		$tache1=$_POST['tache'];
		else $tache1=-1;
		echo"<td><select name='risque' id='risque'>";
		 while($k=$q->fetch())
		  {
		    echo"<option value='".$k['code_risque']."' ";
			if($risque1==$k['code_risque'])echo "selected='selected'";
			echo">".$k['nom_R']."</option>";
		  }
		echo "</select></td></tr>"; 		
     ?>
				<td><input type="submit" value="enregistrer" /></td>
</fieldset>	
	</form>