The Internet affords anonymity to its users, a blessing to privacy and freedom of speech. But that very anonymity is also behind the explosion of cyber-crime that has (1)_____ across the Web.

    Can privacy be preserved (2)_____ bringing safety and security to a world that seems increasingly (3)_____?

    Last month, Howard Schmidt, the nation’s cyber-czar, offered the federal government a (4)_____ to make the Web a safer place—a “voluntary trusted identity” system that would be the high-tech (5)_____ of a physical key, a fingerprint and a photo ID card, all rolled (6)_____ one. The system might use a smart identity card, or a digital credential (7)_____ to a specific computer, and would authenticate users at a range of online services.

    The idea is to (8)_____ a federation of private online identity systems. Users could (9)_____ which system to join, and only registered users whose identities have been authenticated could navigate those systems. The approach contrasts with one that would require an Internet driver’s license (10)_____ by the government.

    Google and Microsoft are among companies that already have these “single sign-on” systems that make it possible for users to (11)_____ just once but use many different services.

    (12)_____ , the approach would create a “walled garden” in cyberspace, with safe “neighborhoods” and bright “streetlights” to establish a sense of a (13)_____ community.

    Mr. Schmidt described it as a “voluntary ecosystem” in which “individuals and organizations can complete online transactions with (14)_____, trusting the identities of each other and the identities of the infrastructure (15)_____ which the transaction runs”.

    Still, the administration’s plan has (16)_____ privacy rights activists. Some applaud the approach; others are concerned. It seems clear that such a scheme is an initiative push toward what would (17)_____ be a compulsory Internet “driver’s license” mentality.

    The plan has also been greeted with (18)_____ by some computer security experts, who worry that the “voluntary ecosystem” envisioned by Mr. Schmidt would still leave much of the Internet (19)_____. They argue that all Internet users should be (20)_____ to register and identify themselves, in the same way that drivers must be licensed to drive on public roads.

答案精析：空处所填词是定语从句的表语，表明system的性质，of… ID card是空处所填词的后置定语，that引导的定语从句的大意为：该系统将是实体钥匙、指纹和带照片的身份证的_____。后文指出该系统会使用smart identity card（智能身份证），可见它是前面三者的等价物，故D选项为正确答案。

错项排除：A、B选项填入原文语义不通，系统不能是信息，也不是对实体钥匙等的干涉，故错误。原文没有提及该系统是否具有娱乐性，C选项缺少原文内容呼应，故错误。