未在form_dropdown选项值Codeigniter中显示的年份

I have this function

public function year() {
    $years = array_merge_recursive(
        array('' => 'Please Select'),
        array_combine(range(date("Y"), 1945), range(date("Y"), 1945))
    );

    return $years;      
}

And on my controller I send to view like

$this->data['byear'] = $this->birthday->year(); 

if ($this->input->post('bd3')) {
    $this->data['bd3'] = $this->input->post('bd3');
} else {
    $this->data['bd3'] = '';
}

$this->data['children'] = array(
    'common/header',
    'common/footer',
    'common/navbar' 
);

$this->load->render('account/register', $this->data);

And then on the view

<?php echo form_dropdown('bd3', $byear, $bd3, array('class' => 'form-control', 'id' => 'birthday'));?>

How ever the option value on view displays numbers from 1 to 72 which is wrong.

Question How can I make sure the option value displays the YEARS?

Change array_merge_recursive to array_replace_recursive

public function year() {
    $years = array_replace_recursive(
        array('' => 'Please Select'),
        array_combine(range(date("Y"), 1945), range(date("Y"), 1945))
    );

    return $years;      
}

Or just add them together.

public function year() {
        $years = array('' => 'Please Select') + array_combine(range(date("Y"), 1945), range(date("Y"), 1945));
        return $years;
    }