为什么嵌套组件不显示？

单击关于，联系人时，它们应该显示在主页组件中，但由于某种原因，这不会发生

import React from 'react'
    import {
      BrowserRouter as Router,
      Route,
      Link
    } from 'react-router-dom'

const BasicExample = () => (
  <Router>
    <div>
      <ul>
        <li><Link to="/">Home</Link></li>
        <li><Link to="/about">About</Link></li>
        <li><Link to="/topics">Topics</Link></li>
      </ul>

      <hr/>

      <Route  component={Home}>
        <Route path="about" component={About}/>
        <Route path="topics" component={Topics}/>
      </Route>
    </div>
  </Router>
)

const Home = () => (
  <div>
    <h2>Home</h2>
  </div>
)

const About = () => (
  <div>
    <h2>About</h2>
  </div>
)

const Topics = () => {
    <div>
    <h2>Topics</h2>
    </div>  
}

export default BasicExample