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.
The answer is A. "the plans of march made by great generals in time of war." The plans they made wasn't as complicated like generals of war, it is an exaggeration.