&lang['example'] in new php. need help

[MrAndrew]

Hello all! My problem is:

I`ve a php, in which describes some functions only. For the example i`ll post a part of the code

echo '<br><br><select name="drop_3" id="drop_3">

      <option value=" " disabled="disabled" selected="selected">Choose Example</option>

      <option value="unknown">Unknown</option>

      <option value="Type Manually Airline Here">Unlisted - Type Manually</option>

      <option value=" " disabled="disabled">---------------------</option>';

Choose Example, Unlisted - Type Manually, Unknown can`t support $lang['choose_example']... Got me error, lang is unknown... How to do this. Help me please! Many thanks!