multiple choice problem about network. Thank you..

20. When light signals travel in different modes (angles) through the fiber-optic cable, they may not reach the destination in exact time interval, this is ________. A. multimode transmission B. propagation conversion C. modal bandwidth D. modal dispersion E. optical interference 21. Modulation is used when A. a node produces text data/signal and the delivery channel relies on analog signaling. B. a node produces sound data/signal and the delivery channel relies on digital signaling. C. a node produces digital data/signal and the delivery channel relies on analog signaling. D. a node produces digital data/signal and the delivery channel relies on digital signaling. E. a node produces digital or analog data/signal and the delivery channel relies on digital signaling. 22. The main equipment room subsystem A. is a demarcation point between the internal network and an ISP network. B. is typically located on the top floor of a building. C. houses workgroup switches that directly connect user stations. D. is the termination point of backbone cabling. E. is the ending point of horizontal cabling.

24. Which is CORRECT regarding the fiber-optic cable? A. The cables properties are defined at the data link layer. B. The cable does not require repeaters to boost signal strength. C. Carriers normally use multimode fibers to develop their backbone infrastructure. D. It uses light signals to move data. E. It is the most popular medium for the access link that connects a host to a switch.