实现VPN的关键技术主要有隧道技术、加解密技术、（）和身份认证技术。

A.入侵检测技术

B.病毒防治技术

C.安全审计技术

D.密钥管理技术

Speaker A: Happy Birthday, Jean.
Speaker B: ().

A. When is your birthday

B. Oh, why have you bought such an expensive necklace for me

C. Happy Birthday to you, too!

D. Oh, a present. How exciting! A necklace! That’s lovely. Thank you.