The data link layer of a device uses sliding windows with a go-back-n algorithm. Suppose it is requested to transmit 7 frames numbered 1 through 7. If the size of the sliding window is 4 frames, what is the content of the sliding window under each of the conditions below? Use * to denote any empty slots in the sliding window. For example, 1,2,** indicates that the sliding window contains only frames 1 and 2. a) No acknowledgements are received. b) Only an acknowledgement for frame 3 is received. c) An acknowledgement for frame 5, then one for frame 4 are received in this order. Briefly justify your answers