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單項選擇題

With PGP, which of the following entity signs a users’s public key?()

A. The sender of the message.
B. The receipient of the message.
C. The sender’s administrator who provides the sender with the PGP program.
D. A third party that belongs to what’s often known as "web of trust", that can verify the relationship between the user and the key.
E. The vendor of the PGP program.

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