change the link code:
<li><a href="../../gas.php?gasID=<?php echo $row_menuwriter_gas["gasID"]; ?>"><?php echo $row_menuwriter_gas["gas_name"]; ?></a></li>
to:
<li><a href="/gas-<?php echo $row_menuwriter_gas["gasID"]; ?>"><?php echo $row_menuwriter_gas["gas_name"]; ?></a></li>