Answer : B
a. Downlink control 3. Sending data from a BS to MD
b. Data communication data rate 4. 2-Mbps
c. The average duration of user's stay in cell 2. Residency Latency (RL)
d. FDDI bandwidth 1. 100 Mbps
Use of Downlink control in Mobile Computing Architecture : The base station subsystem (BSS) is the section of a traditional cellular telephone network which is responsible for handling traffic and signaling between a mobile Device and the network switching subsystem.
So this statement indicates Downlink control is used to Sending data from a BS to MD.
All other options can be eliminated by this one option .I only searched for it