What does letter D represent in the picture above? What principle of relative dating explain this event?

answer: "circumcision is a common procedure in which the skin covering the tip of the penis is surgically removed."

you didn't give any options but heres what i can tell you: an inference is likely to change based on additional observations. the latter is something that you have seen or sensed using your sensory organs while the former is like a conclusion out from what you have observed.

it's diluted or concentrated

in a diluted solution, you can add a lot more solute but in concentrated only a little more can be added