Yet another HTML in PHP question...

So I am working on a PHP project and I've ran into a syntax headache.

Assume $library is a multidimensional array and that all other variables are defined properly.

How do I syntax the following code (it's ugly, I know):

<?php for ($row = 0; $row < $library_size; $row++) {
echo '<option value="'${library[$row]["book_directory"]}'/terms.php">'${library[$row]["nice_name"]}'</option>
} ?>

To print this:
<option value="book_directory/terms.php">Book Nice Name</option>