function validate_form ( )
{
    valid = true;

    if ( document.car.pt.selectedIndex == 0 )
    {
        alert ( "Please select pick-up time." );
        document.car.pt.focus();
        return false;

    }
	if ( document.car.pm.selectedIndex == 0 )
    {
        alert ( "Please select pick-up time." );
        document.car.pm.focus();
        return false;
    }
	
	if ( document.car.dt.selectedIndex == 0 )
    {
        alert ( "Please select return time." );
        document.car.dt.focus();
        return false;

    }
	if ( document.car.dm.selectedIndex == 0 )
    {
        alert ( "Please select return time." );
        document.car.dm.focus();
        return false;
    }
      if ( document.car.group.selectedIndex == 0 )
    {
        alert ( "Please select car group." );
        document.car.group.focus();
        return false;
    }
	
	if ( document.car.pl.selectedIndex == 0 )
    {
        alert ( "Please select pick-up location." );
        document.car.pl.focus();
        return false;
    }
	
       if ( document.car.dl.selectedIndex == 0 )
    {
        alert ( "Please select return location." );
        document.car.dl.focus();
        return false;
    }


    return valid;
}