Displaying list one by one in angular2

<!DOCTYPE html>
<html>

  <head>
    <base href="." />
    <title>angular2 playground</title>
    <link href="//cdn.bootcss.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet">
    <script src="https://unpkg.com/core-js@2.4.1/client/shim.min.js"></script>
    <script src="https://unpkg.com/zone.js/dist/zone.js"></script>
    <script src="https://unpkg.com/zone.js/dist/long-stack-trace-zone.js"></script>
    <script src="https://unpkg.com/reflect-metadata@0.1.3/Reflect.js"></script>
    <script src="https://unpkg.com/systemjs@0.19.31/dist/system.js"></script>
    <script src="config.js"></script>
    <script>
    System.import('app')
      .catch(console.error.bind(console));
  </script>
  </head>

  <body>
    <my-app>
    loading...
  </my-app>
  </body>

</html>

### Angular Starter Plunker - Typescript

System.config({
  //use typescript for compilation
  transpiler: 'typescript',
  //typescript compiler options
  typescriptOptions: {
    emitDecoratorMetadata: true
  },
  paths: {
    'npm:': 'https://unpkg.com/'
  },
  //map tells the System loader where to look for things
  map: {
    
    'app': './src',
    
    '@angular/core': 'npm:@angular/core/bundles/core.umd.js',
    '@angular/common': 'npm:@angular/common/bundles/common.umd.js',
    '@angular/compiler': 'npm:@angular/compiler/bundles/compiler.umd.js',
    '@angular/platform-browser': 'npm:@angular/platform-browser/bundles/platform-browser.umd.js',
    '@angular/platform-browser-dynamic': 'npm:@angular/platform-browser-dynamic/bundles/platform-browser-dynamic.umd.js',
    '@angular/http': 'npm:@angular/http/bundles/http.umd.js',
    '@angular/router': 'npm:@angular/router/bundles/router.umd.js',
    '@angular/forms': 'npm:@angular/forms/bundles/forms.umd.js',
    
    '@angular/core/testing': 'npm:@angular/core/bundles/core-testing.umd.js',
    '@angular/common/testing': 'npm:@angular/common/bundles/common-testing.umd.js',
    '@angular/compiler/testing': 'npm:@angular/compiler/bundles/compiler-testing.umd.js',
    '@angular/platform-browser/testing': 'npm:@angular/platform-browser/bundles/platform-browser-testing.umd.js',
    '@angular/platform-browser-dynamic/testing': 'npm:@angular/platform-browser-dynamic/bundles/platform-browser-dynamic-testing.umd.js',
    '@angular/http/testing': 'npm:@angular/http/bundles/http-testing.umd.js',
    '@angular/router/testing': 'npm:@angular/router/bundles/router-testing.umd.js',
    
    'rxjs': 'npm:rxjs',
    'typescript': 'npm:typescript@2.0.2/lib/typescript.js'
  },
  //packages defines our app package
  packages: {
    app: {
      main: './main.ts',
      defaultExtension: 'ts'
    },
    rxjs: {
      defaultExtension: 'js'
    }
  }
});

//main entry point
import {platformBrowserDynamic} from '@angular/platform-browser-dynamic';
import {AppModule} from './app';

platformBrowserDynamic().bootstrapModule(AppModule)

//our root app component
import {Component, NgModule} from '@angular/core'
import {BrowserModule} from '@angular/platform-browser'
import {FormsModule, ReactiveFormsModule} from '@angular/forms'

@Component({
  selector: 'my-app',
  template: `
    <div class="card" *ngIf="!isLoading">
      <div class="card-block text-md-center" style="padding: 20px">
        <form (ngSubmit)="onSubmit()">
          <fieldset class="form-group hide" *ngFor="let question of questions; let i = index" [class.show]="i == questionIndex">
            <h1>{{question.name}}</h1>
            <div class="form-check">
              <label class="form-check-label">
                <input type="radio" class="form-check-input" [attr.name]="'optionsRadios_'+i" [attr.id]="'optionsRadios1_'+i" value="option1"
                   checked>
                {{question.a_Answer}}
              </label>
            </div>
            <div class="form-check">
              <label class="form-check-label">
                <input type="radio" class="form-check-input" [attr.name]="'optionsRadios_'+i" [attr.id]="'optionsRadios2_'+i" value="option2">
                {{question.b_Answer}}
              </label>
            </div>
            <div class="form-check">
              <label class="form-check-label">
                <input type="radio" class="form-check-input" [attr.name]="'optionsRadios_'+i" [attr.id]="'optionsRadios3_'+i" value="option3">
                {{question.c_Answer}}
              </label>
            </div>
            <div class="form-check">
              <label class="form-check-label">
                <input type="radio" class="form-check-input" [attr.name]="'optionsRadios_'+i" [attr.id]="'optionsRadios4_'+i" value="option4">
                {{question.d_Answer}}
              </label>
            </div>
          </fieldset>
          <p *ngIf="questionIndex == (questions.length - 1)">This is the last one.</p>
          <button type="submit" class="btn btn-primary">Submit</button>
        </form>
      </div>
    </div>
  `,
})
export class App {
  
  private questions: Array<any>;
  private isLoading: boolearn;
  private questionIndex: number = 0;
  
  constructor() {
    
  }
  
  ngOnInit() {
    this.isLoading = true;
    this.questions = [];
    
    // One
    // this.questions.push({
    //   name: `Question_1`,
    //   a_Answer: `A_1`,
    //   b_Answer: `B_1`,
    //   c_Answer: `C_1`,
    //   d_Answer: `D_1`,
    // });
    
    // Two
    for(let i = 1; i < 4; i++) {
      this.questions.push({
        name: `Question_${i}`,
        a_Answer: `A_${i}`,
        b_Answer: `B_${i}`,
        c_Answer: `C_${i}`,
        d_Answer: `D_${i}`,
      });
    }
    
    this.isLoading = false;
  }
  
  private onSubmit() {
    // One
    // var questLength = this.questions.length;
    // if(questLength < 4) {
    //   questLength++;
    //   this.questions.push({
    //     name: `Question_${questLength}`,
    //     a_Answer: `A_${questLength}`,
    //     b_Answer: `B_${questLength}`,
    //     c_Answer: `C_${questLength}`,
    //     d_Answer: `D_${questLength}`,
    //   })
    // }
    
    // Two
    if(this.questionIndex < (this.questions.length - 1)) {
      this.questionIndex++;
    }
  }
}

@NgModule({
  imports: [ BrowserModule, FormsModule, ReactiveFormsModule ],
  declarations: [ App ],
  bootstrap: [ App ]
})
export class AppModule {}