text: import React, { Component } from "react";
  import { Route, Link } from "react-router-dom";
  import Topic from './Topic';
  
  export default class Topics extends Component {
      render() {
          const { url, path } = this.props.match
          return (
              <div>
                  <h2>Topics</h2>
  
                  <ul>
                      <li>
                          <Link to={`${url}/components`}>Components</Link>
                      </li>
                      <li>
                          <Link to={`${url}/props-v-state`}>Props v. State</Link>
                      </li>
                  </ul>
  
                  <Route path={`${path}/:id`} component={Topic} />
                  <Route
                      exact
                      path={path}
                      render={() => <h3>Please select a topic.</h3>}
                  />
              </div>
          );
      }
  }