Iterate over array content without knowing the keys values

Can someone tell me how to iterate over array keys without knowing their values ? For example:

array:3 [▼
  "name" => "AccountId"
  "activated" => "false"
  "type" => "string"
]

I'd like to get a select list with:

<select name="select">
  <option>name: AccountId</option>
  <option>activated: false</option>
  <option>type: string</option>
</select>