A local area network uses the CSMA/CD protocol to implement media access control, with a data transmission rate of 10Mbps, a distance of 2km between host A and host B, and a signal propagation speed of 200 000km/s. Answer the following questions. (a) If host A and host B send data and a conflict occurs, how long does it take at least from the beginning of sending data to the moment when both hosts detect the conflict? How long does it take at most? (Assuming that no other hosts send data during the data transmission between host A and host B.) (6 points) (b) If there is no conflict or error in the network, host A always sends data to host B with a standard maximum Ethernet data frame (1518 bytes), and host B immediately sends a 64- byte acknowledgment frame to host A after successfully receiving each data frame. What is the effective data transmission rate of host A (without considering the Ethernet preamble)? (7 points)