Answer:
It can be (d) instead of (a), because RAKE receiver (R. Price & P.E. Green, ’A Communication Technique for Multipath Channels’, Proc. IRE, vol. 46, 1958, pp. 555-570) exploits multipath diversity to combat fading, thanks to a fundamental time-frequency decomposition of the channel into independent flat fading channels. Normally the question is asked by choosing all that apply (selections a,b,c,d). Here, the worst situation is when we have a frequency selective/fast fading channel. The scenario which suits CDMA Rake receiver. Therewith, (c) and (d) are the correct answers.
Step-by-step explanation: