Woman: Excuse me; could you bring me a glass of water, please
Man: Sorry, but I’m not a waiter.
Question: What does the man mean

A. He wants a glass of water.
B. He won’t do as the woman asks.
C. He can’t wait any longer.
D. He’s looking for the waiter.

消息在发送前，用发送者的私钥加密消息内容和它的哈希（hash，或译作：杂选、摘要）值，能够保证（）。

A、消息的真实性和完整性

B、消息的真实性和保密性

C、消息的完整性和保密性

D、保密性和防抵赖性