Which layer of the OSI reference model is responsible for ensuring reliable end-to-end delivery of data?（）

You download a file from an FTP site on the Internet. What is the highest layer in the OSI model used in this FTP operation?（）

A. Application
B. Presentation
C. Session
D. Transport
E. Internet
F. Data Link
G. Physical

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While troubleshooting a connectivity problem on the network, you issue the ping command from your PC command prompt, but the output shows request times out. At which OSI layer is this problem associated with?（）

A. The data link layer
B. The application layer
C. The access layer
D. The session layer
E. The network layer

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