Now, say you tell a friend what happened with the smooth bricks. She says that because of the way the smooth bricks have interfered with your building process, she can determine what order the chain of bricks was supposed to be in, without even looking at them. However, she does ask you to label each of the smooth bricks with an LED light matching the color of the brick, so that the only bricks she can identify are the ends of each segment. These LED lights labeling the smooth bricks represent

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pigment tracers
phosphate groups
nucleotides