echo Html::activeDropDownList($model, 'category_id', ArrayHelper::map(Category::find()->all(), 'id', 'name'), ['prompt'=>'Select Category']);In this example, `activeDropDownList` creates a dropdown list for the `category_id` attribute of `$model`. The list of options is generated from all the categories stored in the database (using the `Category` model), with the category's `id` as the option value and the category's `name` as the visible label. The `'prompt'` option adds a default 'Select Category' option to the top of the list. The `activeDropDownList` method is part of the `yii\helpers\Html` package.