The ___ attribute in <td> tag used to indicate for how many rows the cell extends.

The attribute in the <td> tag used to indicate for how many rows the cell extends is the "rowspan" attribute. Here's how you would use it:

1. Start by creating a table using the <table> tag.
2. Create a row in the table using the <tr> tag.
3. Within this row, create a cell using the <td> tag.
4. To make this cell extend across multiple rows, add the "rowspan" attribute to the <td> tag. For example, if you want the cell to extend across 2 rows, you would write <td rowspan="2">.

Here's an example of what the full code might look like:

<table>
  <tr>
    <td rowspan="2">This cell extends across 2 rows</td>
    <td>This is a normal cell</td>
  </tr>
  <tr>
    <td>This is another normal cell</td>
  </tr>
</table>

In this example, the first cell in the first row extends across 2 rows, while the other cells are normal and only take up 1 row.