SimpleJSON get Array lenght ?

Hello, i just begin in Unity and C# from a week and i'm facing an issue using the SimpleJSON.

Here is my JSON Scenario in .txt :

 {
     "Intro": {
            "1": [
             "Lina","Salut toi","Happy"
         ],
         "2": [
             "Alphonse","Oui et toi","Happy"
         ],
         "3": [
             "Lina","Tres bien","Normal"
         ],
         "4": [
             "Alphonse","Cool","Happy"
         ]
     "5": [
             "Alphonse","What'up now ?","Questionning"
         ]
     "6": [
             "Alphonse","On va manger au resto ?","Questionning"
         ]
     }
 }

And here the method i use to get what's in each part of my storyline :

 using SimpleJSON;    
 
 public static JSONNode testData; 
 public static TextAsset filejson;
 public static string fileNamejson = "";
 
 public static void define_scenario_lenght()
         {
             string EventNumber = Regex.Replace(Event_Collider.EventColliderName.ToString (), "[^0-9]", "");
             fileNamejson = "Text_JSON/STORY/STORY_JSON_FR";
             filejson = (TextAsset) Resources.Load(fileNamejson);
             testData = JsonParser(filejson.text); 
         
 Debug.Log ("Contenu du Scenar = "+testData.ToString()); //WORK
 Debug.Log ("Taille de L'intro = "+testData["Intro"][0]);
  // WORK
 Debug.Log ("Scenario Intro Length = "+testData["Intro"].length);
  // Don't work because there is no Length define 

So i wanna know if there is a way to get the Lenght of my JSON array ?

I mean get ["Intro"] lenght for instance, because i will dynamically add values in it, so i can't rely on a fix number. (sorry for my crappy english xd).