Parse error: syntax error, unexpected T_LNUMBER in /wiki/LocalSettings.php (MediaWiki v1.11.0 & reCAPTCHA plugin v1.7)

When I tried to install the reCAPTCHA plugin(extension) for MediaWiki, I met the following problem:

Parse error: syntax error, unexpected T_LNUMBER in /wiki/LocalSettings.php

My configuration is

require_once('extensions/recaptcha/ReCaptcha.php");

Replace the above line with the same quotation mark will solve the error (highlight with the red color).

require_once('extensions/recaptcha/ReCaptcha.php');