content: import React from 'react';
  import { BrowserRouter, Route, Link } from 'react-router-dom';
  import Home from './Home';
  import Topics from './Topics'
  import About from './About';
  
  class App extends React.Component {
      render() {
          return (
              <BrowserRouter>
                  <div>
                      <h1>React Router v4</h1>
  
                      <ul>
                          <li><Link to="/">Home</Link></li>
                          <li><Link to="/topics">Topics</Link></li>
                          <li><Link to="/about">About</Link></li>
                      </ul>
  
                      <hr/>
  
                      <Route exact path="/" component={Home}/>
                      <Route path="/topics" component={Topics}/>
                      <Route path="/about" component={About}/>
                  </div>
              </BrowserRouter>
          );
      }
  }
  
  export default App;
  