Codeigniter：下拉“年”部分未显示

Question

foreach($books as $book) {
        $bID = $book->book_id;
        $bName = $book->book_name ;
        $desc = $book->description;
        $author = $book->author;
        $publisher = $book->publisher;
        $pages = $book->pages;
        $pDate = $book->publication_date;
        $price = $book->price;
        $status = $book->status;
        $quantity = $book->quantity;
        $genres = $book->genres;
        $reviews = $book->reviews;
    };


$date = DateTime::createFromFormat("d-m-Y", $pDate);


$data = array(
              'name'        => 'pages',
              'id'          => 'pages',
              'value'       => $pages,
              'style'       => 'font-size:18px',
              'size'        => '35',
              'placeholder' => 'Pages',
            );
    echo form_input($data);
    echo "<br /><br />";

    $months = array('' => 'Month',
                 '1'  => 'Jan',
                 '2'  => 'Feb',
                 '3'  => 'Mar',
                 '4'  => 'Apr',
                 '5'  => 'May',
                 '6'  => 'Jun',
                 '7'  => 'Jul',
                 '8'  => 'Aug',
                 '9'  => 'Sep',
                 '10' => 'Oct',
                 '11' => 'Nov',
                 '12' => 'Dec'
                );
         $days[''] = 'Day';         
         for($i=1;$i<=31;$i++){
            $days[$i] = $i;
         }

         $start_year = date("Y",mktime(0,0,0,date("m"),date("d"),date("Y")-80));
         $years[''] = 'Year';

         for ($i=$start_year;$i<=date("Y");++$i) {
            $years[$i] = $i;
         }
    echo form_label('Publication Date','pDate')."<br/>".
        form_dropdown('days',$days, $date->format("d"), 'required="required"'). " " . form_dropdown('months',$months, $date->format("m"), 'required="required"'). " " . form_dropdown('years',$years, $date->format("Y"), 'required="required"');
    echo "<br /><br />";

我可以知道为什么我的年份部分没有显示任何价值，但是日期和月份部分显示在下拉菜单中，一切正常，除了年份部分。我怎么能解决它？