<table>
  <tr class=que>
    <td>Why did the scientist install a knocker on his door?</td>
  </tr>
  <tr class=ans>
    <td>He wanted to win the No-bell prize!</td>
  </tr>
  <tr>
    <td> Bring the cursor above the question</td>
  </tr>
</table>

.ans {
  background: yellow;
  margin: 0;
  visibility: collapse;
}

.que:hover + .ans {
  visibility: visible;
}

table {
  font: 18px 'crimson text';
  margin: 20px auto auto auto;
}
td{
  padding: 0 6px;
}
.que {
  height: 40px;
  background: springgreen;
  cursor: pointer;
}