假设我有这个JSON：

{
  "achievement": [
    {
      "title": "Ready for Work",
      "description": "Sign up and get validated",
      "xp": 50,
      "difficulty": 1,
      "level_req": 1
    },
    {
      "title": "All Around Submitter",
      "description": "Get one piece of textual content approved in all five areas.",
      "xp": 500,
      "difficulty": 2,
      "level_req": 1
    }
}

我正在尝试通过PHP：

$string = file_get_contents("achievements.json");
$json_a=json_decode($string,true);

$getit = $json_a->achievement['title'][1];

我正在尝试获取成就的第一个“ id” READY FOR WORK。

我该如何解决？