I believe the answer is: c understanding constancy and change throughout the lifespan.
In social settings, developmental science research is being done by observing the change that the subjects experience if being put at a certain time of environment over time. Example of its research would be finding out whether there is a correlation between parents income with performance throughout school years.
It depends. If the museum is famous and popular then there could be more than 100 people there. If the museum is small and unknown, then there could be very small groups. I didn't really understand your question but I hope this helps!
1,2, skip some numbers, 999, 1000