scope - Angularjs ng-repeat and ng-options are not working in select -

i'm trying values $scope in form using select, undefined values, please me.

angular js

in code, call agregarmuestra() when submit form, $scope.nuevo_muestra doesn't match when using select, works input.

.controller('ctrlregm',function($scope, $state, $http){     $scope.tipos = [{"tipo":"sangre"}, {"tipo":"heces"}, {"tipo":"orina"}];     $scope.nuevo_muestra = {};      $scope.agregarmuestra = function() {         console.log($scope.nuevo_muestra); //print empty array         console.log($scope.nuevo_muestra.tipo); //print undefined          $http.post("/muestra", {             tipo: $scope.nuevo_muestra.tipo,          }).success(function(response){             $scope.muestras.push(response);             $scope.$apply();           });     }; } 

html

this doesn't work

<div class="form-group col s12" >    <select ng-options="t.tipo t in tipos track t.tipo" ng-model="nuevo_muestra.tipo">    </select>    <label>el tipo es: {{nuevo_muestra.tipo}}</label> </div> 

this either

<div class="form-group input-field col s12" >    <select ng-model="nuevo_muestra.tipo">       <option ng-repeat="t in tipos" value="{{t.tipo}}"> {{t.tipo}}       </option>    </select> </div> 

but if use input, work, why, why?? :(

<div class="form-group">    <input type="text" class="form-control" name="tipo" ng-model="nuevo_muestra.tipo"> </div> 

it must either be

<select ng-options="t.tipo t in tipos" ng-model="nuevo_muestra"> </select> 

that replace nuevo_muestra selected element of tipos.

or

<select ng-options="t.tipo t.tipo t in tipos" ng-model="nuevo_muestra.tipo"> </select> 

that set nuevo_muestra.tipo tipo of selected element of tipos.

this described in the documentation.

also, success() deprecated long time, , $scope.$apply() useless here.