记帐外汇主要是两国之间签订有关协定，在相互之间使用，故又称为协定外汇。()
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What is uncertain as for the man？
A. Whether to change his major or not.
B. The importance of language skills.
C. His concrete work after graduation.
D. The payment of his tuition.
滑动窗口协议用于()的协议。
A差错控制
B流量控制
C拥塞控制
D链路管理
OSI参考模型中，()层、()层和()层构成了低层开放的网络通信平台。
A物理层
B数据链路层
C网络层
D会话层
What can we learn about the man？
A. He is having a job interview.
B. He is studying hotel management.
C. He is serving a customer.
D. He is preparing for his graduation.
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