Directions：

Read the following text. Choose the best word (s) for each numbered blank and mark A, B, C or D.

     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  across the Web.
     Can privacy be preserved  bringing safety and security to a world that seems increasingly ?
     Last month, Howard Schmidt, the nation’s cyber-czar, offered the federal government a  to make the Web a safer place-a “voluntary trusted identity” system that would be the high-tech  of a physical key, a fingerprint and a photo ID card, all rolled  one. The system might use a smart identity card, or a digital credential  to a specific computer, and would authenticate users at a range of online services.
     The idea is to  a federation of private online identity systems. User could  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  by the government.

     Google and Microsoft are among companies that already have these “single sign-on” systems that make it possible for users to  just once but use many different services.
     , the approach would create a “walled garden” in cyberspace, with safe “neighborhoods” and bright “streetlights” to establish a sense of a  community.
     Mr. Schmidt described it as a “voluntary ecosystem” in which “individuals and organizations can complete online transactions with , trusting the identities of each other and the identities of the infrastructure  which the transaction runs”.
     Still, the administration’s plan has  privacy rights activists. Some applaud the approach; others are concerned. It seems clear that such a scheme is an initiative push toward what would  be a compulsory Internet “driver’s license” mentality.
     The plan has also been greeted with  by some computer security experts, who worry that the “voluntary ecosystem” envisioned by Mr. Schmidt would still leave much of the Internet . They argue that all Internet users should be  to register and identify themselves, in the same way that drivers must be licensed to drive on public roads.