as question said adjacent are in range so ovel represent nodes which are in range. like a is in range of b. for b and c both in range. here range means if b is sending message it can be seen by both a and c. as d and e are not in range so message sent by b cant be seen by a.
so if a send message then b can not send it otherwise it will be collision but d can send the message without any collision because d is not in range so maximum bandwidth = 2L.
(you can se any node which are non adjacent and can send data without collision you will find max 2 nodes can send simultaneously)
