Unification of east and west germany
The answer is a Natural Experiment.
A natural experiment takes place in natural settings and are used when independent variables can't be manipulated directly for ethical/practical reasons, so in this case the toddlers playing. Any effect observed happens naturally. They aren't seen as true experiments as the independent variable (toddlers playing) hasn't been changed deliberately to see effect on dependent variable (aggressiveness).
Answer:
D. An action that is often outside the jurisdiction of a juvenile court
A sandblasted rock could be different in color because sandblasting takes the top layer of the rock (which has been weathered) off.
