4) a) "At low load, pure ALOHA performs better than slotted ALOHA in terms of packet delay"- Refute or validate the statement. [2] b) Why does WLANs not use CSMA/CD - give 2 reasons. [2] c) What problem does the MACA protocol address in WLANS? Name the mechanism by which it solves the problem? [4]