（ ）是网络的心脏，它提供了网络最基本的核心功能，如网络文件系统、存储器的管理和调度等。

A. Thank you
B. It’s my pleasure
C. By the way
D. No, of course not
E. Never mind

A．This tour is the chance of lifetime．
B．It goes all over North America and South America．
C．It looks like you’re dreaming about something．
D．You’ll have to quit school and your job at the store．
E．My agent wants me to go on a tour with Art’s Jazz Band．
F．Have you told anyone about this yet
G．It would be a great opportunity!