[jQuery] question about selectors

[jQuery] question about selectors


there are three 3*3 tables. how to select the first cell in every row
in the first two talbe?
i tried $("table:lt(2) tr td:first"), but failed? who can explain it?
great thanks.
==============================
<table>
<tr>
    <td></td>
    <td></td>
    <td></td>
</tr>
<tr>
    <td></td>
    <td></td>
    <td></td>
</tr>
<tr>
    <td></td>
    <td></td>
    <td></td>
</tr>
</table>
<table>
<tr>
    <td></td>
    <td></td>
    <td></td>
</tr>
<tr>
    <td></td>
    <td></td>
    <td></td>
</tr>
<tr>
    <td></td>
    <td></td>
    <td></td>
</tr>
</table>
<table>
<tr>
    <td></td>
    <td></td>
    <td></td>
</tr>
<tr>
    <td></td>
    <td></td>
    <td></td>
</tr>
<tr>
    <td></td>
    <td></td>
    <td></td>
</tr>
</table>