How can I filter a page using drop down selection?

I have a web page that displays a list of people and their nationality.

<td><?php echo $row['First_Name'] . " " . $row['Last_Name'] ?></td>
 
 <td><?php echo $row['Country'] ?></td>
 

I would like to add a control to the page that allows the user to apply a filter on the country.

Any suggestions on how I should go about it?

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