Consider the figure below, which shows the arrival of 7 frames for transmission at different wireless nodes at times t=0.1,0.9,1.9,2.2,3.6,4.4,4.9> and each transmission requires exactly one time unit. Slotted-ALOHA is used for the nodes to access a shared channel. Which frame(s) below can be transmitted without involving in a collision in their first attempt? 1 2 5 7