4. (15 points) Suppose we only have three nodes (A B C) placed in a row, and each node's signal can only transmit until its immediate neighbors (e.g., A's signal can only reach B and cannot reach C), as shown in the following figure. We assume that RTS/CTS is adopted and every RTS/CTS indicates the expected amount of transmission time. Every node restrains from sending or receiving when hearing RTS/CTS for the period of time indicated in the RTS/CTS packet. A B a) Can the hidden terminal problem be prevented? If yes, illustrate how it is prevented with an example. If not, give an example in which the hidden terminal problem occurs. b) If we assume that a node can send and receive at the same time, can the exposed terminal problem be prevented? If yes, illustrate how it is prevented with an example. If not, give an example in which the exposed terminal problem occurs.