<div id="block_1" style="display:none">
  <input type="checkbox"> experiment A <br>
  <input type="checkbox"> experiment B <br>
  <input type="checkbox"> experiment C <br>
</div>

<div id="block_2" style="display:none">
  <input type="checkbox"> experiment D <br>
  <input type="checkbox"> experiment E <br>
  <input type="checkbox"> experiment F <br>
</div>

<div id="block_3" style="display:none">
  <input type="checkbox"> experiment G <br>
  <input type="checkbox"> experiment H <br>
  <input type="checkbox"> experiment I <br>
</div>