If options.php is a custom template file (which is not a standard file in twentyten), it would look for it in the child theme folder then the parent theme folder if not found in the child theme folder.
You may be referring the the functions.php file, which behaves differently than other template files in that the child file does NOT override the parent file... the child theme functions.php file is executed first then the parent theme functions.php is subsequently executed. This is done automatically by WP when a page is loaded.
You must take care not to duplicate parent theme functions in the child theme functions.php.
