Consider the scenario shown below, in which there are four wireless nodes, A, B, C, and D. The radio coverage of the four nodes is shown via the shaded ovals; all nodes share the same frequency. When A transmits, it can only be heard/received by B; when B transmits, both A and C can hear/receive from B; when C transmits both B and D (but not A) can hear/receive from C; when D transmits, only C can hear/receive from D. Now suppose that node A has an infinite supply of messages that it wants to send to D; there are no other messages in the network. A message from A must first be sent to B, which then sends the message to C, which then sends the message to D. Time is slotted, with a message transmission time taking exactly one time slot, for example, as in slotted Aloha. During a slot, a node can do one of the following: send a message (if it has a message to be forward toward D); (ii) receive a message (if exactly one is being sent to it), (iii) remain silent. As always, if a node hears two or more simultaneous transmissions, a collision occurs and none of the transmitted messages are received successfully. You can assume that there are no bit level errors, and thus, if exactly one message is sent, it will be received correctly by those within the transmission radius of the sender.