Among the following factors, the channel data transmission rate will not be affected（）
A. Signal propagation speed
B. Signal to noise ratio
C. Bandwidth
D. Modulation rate
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Compared with multimode fiber, the main characteristics of single-mode fiber are（）
A. Long transmission distance, high cost and thin core
B. Long transmission distance, high cost and thick core
C. Short transmission distance, low cost and thick core
D. Short transmission distance, low cost and thin core
One of the following network devices that works at the physical layer is（）
A. Hub
Bridge
C. Router
D. Ethernet Switch
Baud rate means（）
A. Number of transmitted signal symbols per second
Bits transmitted per second
C. Number of possible signal changes per second
D. Bytes transferred per second
In the OSI architecture, what directly serves the Application Layer is（）
A. Presentation Layer
B. Conversation Layer
C. Transport Layer
D. Network Layer
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