Answer:
The correct answers are A and C.
Step-by-step explanation:
Letter B is incorrect because talking about the sea creatures all over the world would take longer than 500 words.
Letter D is also incorrect because a detailed study cannot be written in only one page.
Letter E is also incorrect because the past century is a very long period to be analyzed in such a short essay.
On the other hand, letters A and C are correct because their extension can be limited more easily than the others, specially when talking about personal information or a short period of time such as elementary school.