Forgot to mention when we were working on this, but we need to disable the fields we're hiding and enable the fields we're showing. Fields that aren't visible still send their value when submitting the form. Disabling them prevents that.

Here's how it will look:

```javascript
$byMonth.show().attr('disabled', '');
$byDay.hide().attr('disabled', 'disabled');
$byYear.show().attr('disabled', '');
```

Make sure to apply this to the other branches of the `if` too.