Answer:
D. Sai thinking about her first science experiment
By explaining problems and giving solutions! this is the best fit because the other two might make sense at a first glance, but only explaining problems and solutions would be an effective way to teach people how to set up an aquarium by giving them examples of what to do and what not to do whereas the others are just him talking about his aquarium.
I think under yes you should put everuone is different
What are you even talking about?
D because is saying that is urgent